Counting Atoms October 21 st

Let’s Review!  Atoms are made of protons, neutrons, and electrons  Elements are made of the same kind of atom  The number of protons = the atomic number of the element  Chemical symbols on the periodic table either has:  One capital letter  One capital and one lowercase  It NEVER NEVER NEVER NEVER NEVER NEVER has 2 capitals together. Did I say NEVER? I will try to trick you on your test and so will our friends who make the STAAR.

What is an element?  Element = a pure substance; the same kind of atom  Elements can exist as one atom or hundreds of atoms  All atoms of an element are the SAME no matter what the quantity  Elements are only found on the periodic table.  If it is NOT on the periodic table, it is NOT an element  Examples of elements: Oxygen, Nitrogen, Carbon  Not Elements: air, fire, earth, water (any of your game “stuff”)  If you ever answer air, fire, earth, or water I will make you do text book work until you remember the above point. 70 pages await you if you choose the wrong answer.

Molecules & Compounds Molecules = more than 1 atom  Can be a molecule of an element  You can have 2 atoms of hydrogen to make a molecule of pure hydrogen H 2  It is not one atom, so it is a molecule  It is not a compound because there is only one type of element Compounds = more than one element  Think “complicated” for compound  Water, H 2 0 is a compound because there are 2 elements (hydrogen and oxygen) in it.

How can you count atoms in molecules and compounds? Subscripts = add The small number to the bottom right of the chemical symbol is called the subscript. Sub = under Script = Writing To count atoms:  Look at the subscripts  No subscript? Write in the number 1  You may need to add the subscripts depending on what the question is

Let’s Practice: What elements are here? 1. H 4 2. H 2 O 3. CH 4 4. NaCl 5. CaCO 3

Let’s Practice: How many of each element? 1. H 4 2. H 2 O 3. CH 4 4. NaCl 5. CaCO 3

Exit Practice: Which elements are present and how many of each element: 1. CO 2 2. LiCl 3. H 2 O 2

Coefficients and counting atoms  Coefficients = multiplying  It’s the large number in the front; I call it the “Mamba Jamba”  In math, it looks like this: 2x 3 The number two is the coefficient and 3 is the superscript  Distributive property (if you don’t know about it yet, get ready….its coming)  In chemistry, you will use the coefficient to multiply all of the subscripts  You distribute the coefficient to all of the elements  Each element gets multiplied by the coefficient  The coefficient tells you how many molecules you have

Doodle this: 3 water molecules Draw what Mrs. Szymanski does Wouldn’t it be lame to have to write: H 2 O + H 2 O + H 2 O Instead, we write: 3 H 2 O

You can do it two ways! You’ve got options!!! Its your lucky day. Way #1: 3 CaCl 2  Multiply all elements by 3  Calcium = 3  Chlorine = 6  Total atoms = = 9 Way #2: 3 CaCl 2  Add all of the elements first  Calcium = 1  Chlorine = 2  = 3  Multiple the answer by the coefficient:  3 times 3 = 9

Practice with Coefficients: 1. 3 H H 2 O 3. 4 CH NaCl 5. 5 CaCO 3

Exit Ticket: What is the difference between a subscript and a coefficient?