Presentation on theme: "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."— Presentation transcript:
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 = 6 + 3 = 9 Way #2: 3 CaCl 2 Add all of the elements first Calcium = 1 Chlorine = 2 1 + 2 = 3 Multiple the answer by the coefficient: 3 times 3 = 9
Practice with Coefficients: 1. 3 H 4 2. 2 H 2 O 3. 4 CH 4 4. 2 NaCl 5. 5 CaCO 3
Exit Ticket: What is the difference between a subscript and a coefficient?