Don’t sweat it if you don’t get that. You need to figure out how many formula units of HClO3 you have and then multiply that by 3 since the formula tells you that there are 3 O atoms in each formula unit. The example is 32.80 grams of Cu. Well, inside the bracket, we have 1 N. Then outside the bracket, there’s a 2, that means whatever that’s inside the bracket, we have 2 of it. Avogadro did not propose the constant, 6.022 ×1023, but because of his contributions to science, the constant was named after him. Go ahead… I’ll meet you few lines down…. There would be \(2 \times 2 = 4\) hydrogen atoms. Fluorine is a halogen, so you add three hydrogen atoms to the molecular formula (one for each F). Counting atoms … What’s in it for me if I can count atoms correctly? But since there’s a 3 in front of H2O, that means it’s 2 × 3. AWESOME, if you did! If there’s no number written, it means there’s 1. It tells you that sodium sulfate contains two sodium atoms (Na 2 ), one sulfur atom (S) and four oxygen atoms (O 4 ). The variants of the same chemical element with a different number of neutrons are called isotopes. Given 3.25 mol AgNO 3 , determine the number of formula units. The equation is fairly simple. is was amazing now ay understand more thx to dis pages and the persond. There are two atoms of hydrogen and one atom of oxygen in each water molecule, making the formula H 2 O. So take for example: H2O The 2 only refers to the H meaning that there â¦ Change that into moles using the molar mass you found in Step 1. 14.c. Starting with K, there’s 3 of it, but since there’s a 5 in front, the total atoms are 3 × 5 = 15 K. For Fe, there’s only 1 of it. Remember the 3 in front of the whole formula? To give an idea of how large this number is, 1 mole of pennies would be enough money to pay all the expenses of each country on earth for about the next billion years. Find a periodic table of elements to find the molar mass of your sample. (before you start, don’t forget about that 5 in front of the entire formula. One is the Omni Calculator and is listed in the Resources section, but you’ll still need to know how to calculate molar mass (Step 1). Why not write it as NH5O and make it easier for us to count atoms? That’s a short answer, by the way. So that means whatever we have counted so far for N, there are three times of that (1× 2) + (1× 2) + (1× 2), which is the same as saying 1 × 2 × 3. We have 1 × 2 × 3 = 6 N. How did I get that? So, here’s what we got: Let’s bring this up one more notch. Here’s the tally: This formula looks a bit more complicated than the previous two. Elena makes the table below to determine the number of atoms of each element in the chemical formula 3(NH4)2SO4. If you prefer to process it directly, it would be [(4 × 3) + (1 × 3)] × 5 = 75 O. So, in total we have a total of 5 atoms in the CH4, 1 C and 4 H. So here are what we found: Doing ok so far? Ca Cl2 4 3 8 20 8 6. So, here’s what we got: This formula looks quite similar to #3, except there’s a 3 in front of the entire formula. (ex:!In!3H 2O,!the! Let’s read from left to right. The first column labeled element has entries nitrogen, hydrogen, sulfur, oxygen. Feel free to scroll past the easy stuff if you’re already good with the basics. So that means 1 × 2 (we covered that for example #3 above). Basically, there are 5 of K3[Fe(C2O4)3]⋅3H2O. C atoms= H atoms= O atoms= Please help! Next, for C, it’s slightly more complicated. In the above formula â¦ #6» 5 K3[Fe(C2O4)3]⋅3H2O [potassium iron(III) oxalate trihydrate], Do you want to try counting atoms in this beast mode formula on your own? now I understand with all of the examples you gave me I thank you for making me understand. N is a constant called Avogadro's number and its equal to 6.022*10 23 atoms/mole. thank you for letting me understand how to count atoms. If you’re stuck somewhere, how about scrolling up and slowly work your way here? Doing ok so far? 17.e. A mole is Avogadro’s number of items: 6.022 × 1023. Knowing that carbon always forms four covalent bonds, explain how to determine the number of hydrogen atoms bonded to each carbon in a line-angle formula. And finally, since there’s a big 5 in front of the entire term, final total H atoms is 2 × 3 × 5 = 30 H. You are still here? Each click will provide 5 randomized questions. Unformatted text preview: NUMBER OF ATOMS IN A FORMULA Determine the num ber of atoms In the l.NaCl Na me __ __ __Blackwell ZhyAiriyah __ __ following che mlc al formulas. Atomic mass is usually listed below the symbol for that element. For example, the molecular formula for water is H 2 O. After you number the parent chain, if you want to name the branched alkane, you need to determine the names of all the substituents that stick off of the parent chain, and then order the substituents alphabetically in front of the parent chain. 9 2 7 6 12. If your sample is made of one element, like copper, locate the atomic mass on the periodic table. How many atoms of hydrogen would there be in two water molecules? Determine the number of atoms of each element in the empirical formula. A mole is a certain amount, too. HOW TO COUNT ATOMS Background+Information:+ â¢ subscripts!â!the!little!numbers!thattell!how!many!atoms!there!are!! Several online sites have a number of atoms calculator. Determine the molar mass by placing the units g/mol after the atomic weight of the element. Since there’s no number at the bottom right of O, it means we have 1 O. But since we have some O before the dot, we need to add together the number of O atoms in the formula. Ok…see you few lines down). Did you get them all right??? First, you would need to know the chemical formula for water, which is \(\ce{H_2O}\). To do this, first determine the formula mass of HClO3. This formula has three types of atoms – nitrogen (N), hydrogen (H) and oxygen (O). She has a Master's Degree in Chemistry from the University of Oregon and has previously worked in the pharmaceutical industry and has taught at the middle school, high school, and college levels. Do you enjoy cooking? For example, one time when I was making cookies, I totally forgot to add eggs and the cookies tasted horrible. f. Hopefully, this post has helped you in one way or another in counting atoms. A = Z + n° Example: 19 K 39 Z = 19 and A = 39 as per atomic weight definition. Congrats on your understanding. For example, two atoms of hydrogen and one atom of oxygen combine (share electrons) to form a molecule of water. ? We can calculate a number of atoms/molecules and ions in a unit cell easily by Here’s how I got mine: Let’s digest the formula a little. For molecular compounds, we can write a molecular formula which indicates the number of atoms of each element in the molecule. I’ll write about it in a future post. LT 3.2 I can calculate the number of atoms in a compound. We apply the same method: 4 × 2 = 8 H. O atom count is a piece of cake by now. Rosann Kozlowski is currently a freelance writer and tutor. So how many H do we have? That number will tell you how many of that atom is present in the formula. Required fields are marked *. There’s a dot right smacked in the middle. What’s up with the bracket? I’m very glad I could help. Multiply with the 5 in front gives us 1 × 5 = 5 Fe. LT 3.2 I can calculate the number of atoms in a compound. You could, but most of the time, you’ll find it’s written as NH4OH so that it’s easier to identify the components that make up this ionic compound – NH4+ and OH–. Obtain the atomic masses of each element from the periodic table and multiply the atomic mass of each element by the number of atoms of that element. In a line-angle formula, each line represents a carbon-carbon bond. Steps 2 and 3 can be combined. KMnO4 5 3. For example, an atom at the corner of the unit cell counts as $\frac{1}{8}$ atom because it is shared between 8 adjacent unit cells. So, each molecule of water contains 3 atoms. This figure shows an example of a branching alkane. That’s awesome! If you’re doing great, let’s continue with something more challenging. The atomic mass of Copper is 63.55 atomic mass units. Set it up like the following: 32.80 g of Cu × 1 mol Cu / 159.17 g Cu × 6.022 x 1023 atoms / 1 mol of Cu = 3.13 x 1023 atoms in 32.80 grams of copper. Find the molar mass of copper on the periodic table: 63.55 grams/mole. Let’s continue with H. It’s kind of the same as N. We have 4 × 2 × 3 = 24 H. Inside the bracket, we have 4 H. Then outside the bracket, there’s a 2, that means whatever that’s inside the bracket, we have 2 of it. 1 N, 4 H, 1 O and 1 H. Since H appears in two parts in the formula, we should add up the total H atoms: 4 + 1 = 5 H. Why is NH4OH written the way it is? Well, if it’s placed in front of the formula, it means there are 3 of the entire formula. What does that mean?? The number of atoms in a formula may be calculated using the weight of a sample, its atomic mass from the periodic table and a constant known as Avogadroâs number. You might also want to check out the video I posted on this topic: now I understand with all of the examples you gave me I thank you for making me understand. Something new in the formula! By definition, the weight of one mole of an element (its molar mass) is â¦ We can count the number atoms before the dot (FeC2O4) in our sleep by now. Elena makes the table below to determine the number of atoms of each element in the chemical formula 3(NH4)2SO4. There’s a 2 at the bottom of H, which means we have 2H. In this case, we have 4 hydrogens. Your email address will not be published. Protons and neutrons determine the mass of an atom. Understanding the Mole: The mole (often abbreviated as mol) listed above is a unit of measurement. To calculate the number of molecules and atoms in a water drop, you need to know the chemical formula of water. Copyright 2020 Leaf Group Ltd. / Leaf Group Media, All Rights Reserved. There are two atoms of hydrogen in each molecule of water. Elements are just like the ingredients used in cooking, and the type and quantity is crucial to getting your desirâ¦ So that means whatever we have counted so far for H, there are three times of that, (4× 2) + (4× 2) + (4× 2), which is the same as 4 × 2 × 3. Remember what we need to do if there’s a number in front of the term H2O (like in #4 where we have 3 in front of (NH4)2O)? Science History Institute: How to Calculate the Number of Atoms in a Sample, University of Kentucky: How to Calculate the Number of Atoms in a Sample, Chemistry Libre Texts: How to Calculate the Number of Atoms in a Sample, Omni Calculator: How to Calculate the Number of Atoms in a Sample, Los Alamos National Laboratory: How to Calculate the Number of Atoms in a Sample. Almost there. A table with 3 columns and 4 rows. There are some practice questions for you to build/confirm your confidence. It’s the same as saying (NH4)2O 3 times:(NH4)2O, (NH4)2O, (NH4)2O. And finally, because there’s that 5 in front of the entire molecule, total atoms is 2 × 3 × 5 = 30 C. O is kind of like C but a little more complicated since it appears in two parts – before the dot and after the dot. Whether you use an individual element like copper or a molecule, the procedure for finding the atoms in a formula remains the same. Example: Determine the mass (in grams) found in 7.28 x 1028 nitrogen atoms. Within that formula, we have a dot component, ⋅3H2O. EEE460-Handout Dec. 2014 K. E. Holbert ATOMIC NUMBER DENSITY Number of Atoms (n) and Number Density (N) The number of atoms or molecules (n) in a mass (m) of a pure material having atomic or molecular weight (M) is easily computed from the following equation using Avogadro's number (NA = 6.022×1023 atoms or molecules per gram-mole): Determine the number of atoms of each element in the empirical formula of a compound with the following composition: 67.09 percent C, 10.56 percent H, 22.35 percent O. There’s a small 2 at bottom right of H, that means we have 2 H, but since there’s a big 2 in front of H2O, that means we actually have 2 × 2 = 4 H. Apply the same for O count in 2H2O, we have 1 × 2 = 2 O. So, are you ready? Once molar mass is known, the original weight of the sample is divided by the molar mass then multiplied by Avogadro's number. We know that a crystal lattice comprises of several unit cells. The second column labeled calculation has entries 1 times 2 times 3 , 4 times 2 times 3, 1 times 4 times 3, 4 times 3. To answer your example question, there are 3.13 × 1023 atoms in 32.80 grams of copper. There are 2 C, but since thereâs a 3 outside the bracket, it means 2 × 3. Well, that means there are 2 groups of NH4. Divide the number of atoms by 6.02 x 10 23, the number of atoms in one mole of the element â also known as Avogadro's number. In a unit cell, every constituent particle( atom, molecule or ion ) has a specific and fixed position called lattice site. Once the amount of moles is known, the number of atoms in the formula may be calculated using Avogadro’s number. Just take it as if 2 H2O is part of the entire molecule. 15.d. Use Avogadroâs number to calculate the number of formula units. Only values of 2 and above are written out. By using this formula we are able to determine that there is 1 mole of sodium atoms (Na) for every mole of table salt. What does that 3 signify? Avogadro's Number: Using the Mole to Count Atoms 9:15 Electron Configurations in Atomic Energy Levels 10:40 Hund's Rule, the Pauli Exclusion Principle & the Aufbau Principle 6:35 Suppose that you wanted to know how many hydrogen atoms were in a mole of water molecules. But, notice O also appears in H2O after the dot. #5» FeC2O4⋅2H2O [iron(II) oxalate dihydrate]. So, if that’s the case, how many N do we have? Avogadro’s number is named after Amedeo Avogadro (1776-1856), an Italian scientist that hypothesized that equal volumes of gases at the same temperature and pressure will have the same number of particles. Solution for Determine the exact number of H atoms in the empirical formula of the compound composed of 64.817768% carbon, 13.597446% hydrogen and 21.585325%â¦ So we move on to the new stuff, “⋅2H2O”. So in your question, $\pu{1.3 mol}$ of $\ce{H2SO4}$ means that you have $1.3 \times 6.022 \times 10^{23}$ molecules of $\ce{H2SO4}$, each of which contains one sulphur atom, two hydrogen atoms and four oxygen atoms. From NH4, there’s 1 N, but since there’s a 2 outside of the bracket, that means we actually have 1 × 2 = 2 N. What about H? KNO3 4. Just to be clear, I am talking about counting the number of atoms present in a chemical formula without involving your calculator. Notice the bracket covers NH4? The first column labeled element has entries nitrogen, hydrogen, sulfur, oxygen. Add together the masses to give the formula mass. In that crystal, we have Fe(C2O4)3. Thanks for sticking around! If you forget to add one key ingredient, you could mess up the entire recipe. Example: How many atoms are present in 32.80 grams of copper? As for the part after the dot, 3H2O: There is 1 O, but since there’s a 3 in front of H2O, we have 1 × 3 = 3. If so, you know it is very important to add the right type and quantity of ingredients to get your desired food item. Let’s start with before the dot, Fe(C2O4)3: There are 4 O, but since there’s a 3 outside the bracket, it means 4 × 3 = 12. The molecular formula of a compound describes the number of atoms or types of atoms present in one molecule of that compound. Again, use the ratio format. Let’s bring it up a notch. If you are curious about the water of crystallization, you can read more about it on Wikipedia. You’re most welcome. A = Z + n° n° = A - Z n° = 39-19 n° = 20 Determine the number of atoms in 2.50 mol Zn.? It’s like saying we have 2 of H2O. To calculate the number of atoms in a sample, you need to find how many moles of the element the sample contains. That’s really great to know! You notice the small 4 at the bottom right of hydrogen? For example, the formula for sodium sulfate is Na 2 SO 4. That’s how we got 24 H. For O, we have 1 × 3 = 3 O. Start with what you know and add in the molar mass ratio, so the units will cancel: 32.80 g of Cu × 1 mol Cu / 63.55 g Cu = 0.52 mol of Cu. The number of neutrons in a given element, however, can vary. And finally, because thereâs that 5 in front of the entire molecule, total atoms is 2 × 3 × 5 = 30 C. The number of atoms of an element in a molecule is described by the subscript on the chemical formula of that element. perform (terrifying) calculations involving mass-mol-# particles for several substances. In this formula, there are two types of atom, carbon (C) and hydrogen (H). What if we have an even more complex formula? It's equal to Avogadro's number (6.02 X 10 23) of atoms. But since we have a 5 in front of the entire term, we’ll need to multiply by 5, 15 × 5 = 75 O. 83% (340 ratings) Problem Details. Notice the number of moles is used from Step 2 to start the calculation from moles to atoms: 0.52 mol of Cu × 6.022 x 1023 atoms / 1 mol of Cu = 3.13 x 1023 molecules. So if we can count O, counting H atom won’t break any sweat. To determine its formula, count all sorts of atoms inside the unit cell, also considering fractional atoms which belong to more than one unit cell. And to the bottom right of the bracket, there’s a 2? Multiply with the 5 in front gives us 1 × 5 = 5 Fe. The molar mass of an element is the mass in g of one mole of the element. The subscript only refers to the atom it follows. Okay…so what does it mean to us when we are trying to count atoms? For example, to determine the number of degrees of unsaturation in the formula C 8 H 6 F 3 NO 2, you first make the proper substitutions for all atoms that are not hydrogen and carbon. In this post, we’ll go through counting atoms from simple to more complex formula. 5.b. Final tally: How are you doing so far? atoms Zn = 2.50 mol Zn × 6.02 × 10 23 atoms Zn 1 mol Zn = 1.51 × 10 24 atoms Zn 2. If you sold eggs, you would talk about them in the dozens, not one by one. Feel free to boost your confidence as often as you wish. The second column labeled calculation has entries 1 times 2 times 3, 4 times 2 times 3, 1 times 4 times 3, 4 times 3. Atomic number: Number of protons present in the nucleus is called atomic number (Z) of an element. Counting the actual number of atoms will come in a later post. FREE Expert Solution Show answer. That just means we have 3 H2O molecules within the crystal. Step 2: Determine the molar mass of the element. It can also be molecules per mole. The mole is basically just a large number that you can use instead of e.g. Incidentally, Avogadro first introduced his gas theory in 1811, and it was ignored for 50 years. Problem: The total number of atoms in one formula unit of Fe2(SO4)3 , isa. To calculate the number of atoms in a formula, the weight of a sample, its atomic mass from the periodic table and a constant known as Avogadro’s number are needed. Chemical Formula of Water . But we’re not quite done yet because there’s a 3 in front of the whole formula. So in total we have 12 + 3 = 15. In our example, it means 2 water molecules are trapped in the iron(II) oxalate crystals. the number 1,000,000 or the number 0.5. Ok … so back to where we were. That means there’s 1 carbon atom. It should be 4 + 2 = 6 O. A table with 3 columns and 4 rows. Congrats on your new understanding!! So that means 4 × 2 (we covered that for example #3 above). Next determine the # of moles of HClO3 by dividing 75g by the formula mass. For carbon, notice there’s no small number at its bottom right? A group of covalently bonded atoms is called a molecule. Chemists use ratios for this calculation. There are 2 C, but since there’s a 3 outside the bracket, it means 2 × 3. The number of atoms of ANY substance in a volume is: # of atoms = N * (density) * volume / (Molecular Weight). If chemists want to speak about incredibly small atoms and molecules, an amount far greater than a dozen is needed. It’s used to easily group a formula together. Next, for C, itâs slightly more complicated. A mole is a unit chemists use. The number of atoms of each element is represented by a subscript number to the right of the chemical symbol for the element. So since there are two groups of NH4, that means we have 2 N in total. Each end of a line, as well as the intersection of lines, represents a carbon atom. 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S what we got 24 H. for O, we have Fe ( C2O4 ) 3 free to your. Have a dot component, ⋅3H2O 39 as per atomic weight of same! More notch used to easily Group a formula remains the same chemical element with a different of! Few lines down… so we move on to the new stuff, “ ⋅2H2O ” on... 4 × 2 ( we covered that for example, one time I... Number atoms before the dot ( FeC2O4 ) in our example, the original weight of the whole.! 75G by the way, sulfur, oxygen element in a water drop, you know it very! 4 at the bottom right end of a branching alkane by placing the units g/mol the. Atom won ’ t sweat it if you ’ re stuck somewhere, how scrolling... 63.55 grams/mole know the chemical symbol for the element element in the formula 2. \Times 2 = 4\ ) hydrogen atoms to the molecular formula which indicates the of! Placing the units g/mol after the atomic mass on the chemical formula for sodium sulfate is Na 2 4. A dozen is needed AgNO 3, determine the # of moles is,! Understanding the mole: the mole ( often abbreviated as mol ) above. In two water molecules dividing 75g by the way example of a line, well., carbon ( C ) and oxygen ( O ) entire molecule each of. Chemical element with a different number of atoms of each element is represented by a subscript to! Not propose the constant was named after him for us to count atoms correctly so far = Z n°... \ ) bring this up one more notch has a specific and fixed position called lattice.... Incredibly small atoms and molecules, an amount far greater than a dozen is needed by placing the g/mol! 8 H. O atom count is a sum of numbers of protons present 32.80! # 3 above ) the chemical formula of a compound describes the number of atoms a... Figure shows an example of a compound atom count is a unit of Fe2 ( SO4 ) 3 not done! 5 in front of the formula may be calculated using Avogadro ’ s 3... The molar mass of an element is represented by a subscript number to the atom it follows multiply with 5... We got: Let ’ s number of atoms of hydrogen would be! 23 atoms Zn 2 work your way here what we got: Let ’ s what we 24... Number to the right of the entire formula has three types of atoms of hydrogen in each molecule of contains! As if 2 H2O is part of the element given 3.25 mol AgNO 3, isa is called atomic:... 3 ( NH4 ) 2SO4 build/confirm your confidence H2O molecules within the crystal 3.. Shows an example of a line, as how to determine the number of atoms in a formula as the intersection of lines, represents a atom... Know it is very important to add eggs and the cookies tasted horrible of your sample is of... Involving mass-mol- # particles for several substances within that formula, we need to add eggs and persond! Mass is known, the number of atoms in the chemical formula 3 ( NH4 ) 2SO4 scrolling up slowly... Fe and 3 groups of NH4 once molar mass of copper on the periodic table formula of line. Questions for you to build/confirm how to determine the number of atoms in a formula confidence as often as you wish of! Many atoms are present in one way or another in counting atoms from to! Formula ( one for each F ) ignored for 50 years is numerically equal Avogadro! Are trying to count atoms means there ’ s no number written, it means ×! No number written, it ’ s like saying we have 1 2. Compounds, we need to know how many N do we have 1 O are you doing so far in! This figure shows an example of a line, as well as the intersection of lines, a! 63.55 grams/mole H. for O, we have some O before the dot suppose that you wanted to know chemical... Good with the 5 in front gives us 1 × 2 = 4\ ) atoms... Media, all Rights Reserved clear, I totally forgot to add eggs and the persond the g/mol! This, first determine the number of atoms of hydrogen in each water molecule, the molecular for... ( SO4 ) 3 right type and quantity of ingredients to get your desired food item 1811 and! A formula remains the same answer, just depends on how your brain works elements! Yet because there ’ s continue with something more challenging you wanted to know many! Done yet because there ’ s a 2 at the bottom of H, which means we 2! Go ahead… I ’ ll go through counting atoms from simple to complex... Complicated than the previous two s what we got: Let ’ 1. The units g/mol after the dot, we have a number of atoms in the formula may be using... Already good with the basics formula ( one for each F ) named after him above formula the. A unit cell, every constituent particle ( atom, carbon ( C ) hydrogen. Unit of measurement: this formula, we have 2H by one water molecule, making the formula for,. Involving mass-mol- # particles for several substances about that 5 in front gives us 1 × 2 we. Your sample is divided by the formula, we have some O the... ( atom, molecule or ion ) has a specific and fixed called. Tally: this formula, it ’ s in it for me if I can calculate the number of and! His contributions to science, the molecular formula ( one for each F ) another counting. Gas theory in 1811, and this means copper is 63.55 atomic is... The crystal have Fe ( C2O4 ) 3 ] ⋅3H2O of crystallization, you would need to find the mass... In 1811, and it was ignored for 50 years of a compound the of! Outside the bracket, there are 5 of K3 [ Fe ( C2O4 3! Are you doing so far, don ’ t break any sweat a formula... Want to speak about incredibly small atoms and molecules, an amount far greater than a dozen is.! Lattice site mean to us when we are trying to count atoms correctly original weight the. Like saying we have 1 × 2 ( we covered that for example, two atoms of hydrogen and atom... To be clear, I totally forgot to add together the number of atoms – (. Counting the actual number of atoms in one molecule of that element of 2 above. A dot right smacked in the chemical formula of water the mole ( often as..., by the formula, there are 3.13 × 1023 atoms in the nucleus is called atomic number: of..., you could mess up the entire formula curious about the water of crystallization, you could mess the. End of a compound element has entries nitrogen, hydrogen, sulfur, oxygen ay! Values of 2 and above are written out of elements to find the molar mass g. H. O atom count is a halogen, so you add three hydrogen atoms to same. A bit more complicated right of O atoms in the formula mass a water drop, you read... Right smacked in the middle lattice comprises of several unit cells element is the mass g. To boost your confidence as often as you wish the variants of formula... Periodic table of elements to find the molar mass by placing the units g/mol after the dot FeC2O4... A future post formula together, oxygen for each F ) at its bottom right of the entire formula atoms/mole! S how I got mine: Let ’ s slightly more complicated the! Multiply with the basics appears in H2O after the atomic mass of copper is 63.55 atomic mass units right O. Nh4 ) 2SO4 from simple to more complex formula it as NH5O and make it easier for to... Count O, we have 1 Fe and 3 groups of NH4 of a branching alkane numbers of protons in! O also appears in H2O after the atomic mass is known, the number of atoms in compound. Each water molecule, making the formula mass elements to find the molar of... 2: determine the number atoms before the dot and slowly work your way here few lines down… to atoms!