Unit 9 – Chemistry (Atoms, Elements, Periodic
Table, Bohr Models, and Chemical Reactions)
NYS Standards:
3.3a All matter is made up of atoms. Atoms are far too small to see when a light microscope.
3.3b Atoms and molecules are perpetually in motion. The greater the temperature, the greater the
motion.
3.3c Atoms may join together in well-defined molecules or may be arranged in regular geometric
patterns.
3.3d Interactions among atoms and/or molecules result in chemical reactions.
3.3e The atoms of any one element are different from the atoms of other elements.
3.3f There are more than 100 elements. Elements combine in a multitude of ways to produce
compounds that account for all living and nonliving substances. Few elements are found in their
pure form.
3.3g The periodic table is one useful model for classifying elements. The periodic table can be
used to predict properties of elements (metals, nonmetals, noble gases).
The Atom
-Three Parts
1. Protons = Positive Charge
2. Neutrons = Neutral Charge
3. Electrons = Negative Charge
Protons + Neutrons = Nucleus
-Elements
A pure substance that cannot be broken down into
other substances.
Examples: Gold, Copper, Oxygen, Nitrogen
-Protons, Neutrons, Electrons
 All atoms we draw will have equal protons and
electrons.
 # of protons = look at the atomic number (the
smaller number)
 # of electrons = look at the atomic number
 # of neutrons = subtract the atomic number from the
atomic mass.
Practice
2
= 2 Protons
11
= 11 P
He = 2 Neutrons
H
= 12 N (23.0 - 11 = 12)
4.0 = 2 Electrons
23.0 = 11 E
21 = 21 P
19 = 19 P
Se = 24 N (45.0 – 21= 24)
K = 20 N (39 - 19 = 20)
45.0 = 21 E
39.0 = 19 E
The Periodic Table Parts
 Periods – Move from left to right across the
periodic table (7 Periods).
 Groups – Move from top to bottom down the
periodic table (18 Groups).
The Periodic Table of Elements
Group 1





Alkali Metals
Li, Na, K, Rb, Cs, Fr
Metals
Very Reactive
1 Electron in outer level
Group 2





Alkaline-Earth Metals
Be, Mg, Ca, Sr, Ba, Ra
Metals
Reactive, but not as reactive as Alkali Metals
2 Electron in outer level
Groups 3 – 12
 Transition Metals
 1 or 2 Electron in outer level
Lanthanides and Actinides
 Lanthanides: elements La through Lu
 Actinides: elements Ac through Lr
Groups 13 – 16 with Metalloids
Group13





Boron Group 13
B, Al, Ga, In, Tl
Reactive
Solid at Room Temperature
3 Electron in outer level
Group14





Carbon Group 14
C, Si, Ge, Sn, Pb
Reactivity varies among the elements
Solid at Room Temperature
4 Electron in outer level
Group15





Nitrogen Group 15
N, P, As, Sb, Bi
Reactivity varies among the elements
All but nitrogen are Solid at Room Temperature
5 Electron in outer level
Group16





Oxygen Group 16
O, S, Se, Te, Po
Reactive
All but oxygen are Solid at Room Temperature
6 Electron in outer level
Group17





Halogens
F, Cl, Br, I, At
Very Reactive
React violently with alkali metals to form salts
7 Electron in outer level
Group18





Noble Gases
He, Ne, Ar, Kr, Xe, Rn
Unreactive
Colorless, odorless gases at room temperature
8 Electron in outer level (2 for Helium – He)
Hydrogen





Hydrogen stands alone
H
Reactive
Colorless, odorless gas at room temperature
Explosive reaction with oxygen
Groups are arranged due to all members top to bottom
having similar Physical and Chemical properties.
Chemical Reactions
Every Reaction Involves Energy
1. During a reaction…bonds absorb energy and break.
2. New bonds form…energy released.
Symbols in Chemical Reactions
= Gas Formation
= Gas Formation
Heat = Heat is given off
Energy = Light Energy, Electrical Energy,
Thermal Energy
What is a Chemical Reaction?
Chemical Reaction – The process by which one or
more substance undergo change to produce one of
more different substances.
How to identify a chemical reaction has occurred or is
happening?
1. Gas Formation
3. Color Change
2. Solid Formation
4. Energy Change
What are the parts of a chemical reaction?
1. Reactants – Starting materials of a chemical
reaction.
2. Products – Substances formed
C + O2
Reactants
CO2
Products
Chemical Reactions Must Be Balanced!!!!
It’s a Law!!!
The Law of Conservation of Mass
-Mass is neither created nor destroyed in
ordinary chemical reactions.
Exothermic Reaction
 Chemical reaction in which energy is released or
removed.
 Energy is in the products in an Exothermic
Reaction.
Endothermic Reaction
 Chemical reaction in which energy is absorbed.
 Energy is in the reactants in an Endothermic
Reaction.
Current Atomic Structure
 Current atomic structure is attributed to scientist Neils
Bohr.
 Bohr theorized that electron motion could not be predicted,
but that we would determine where we could find them.
 Bohr called these areas…Electron Clouds
Electron Clouds
 There are 7 clouds, but we will only cover 4
because they can overlap becoming too
advanced.
 Each cloud is limited to how many electrons
it can hold.
o Cloud 1 = 2
o Cloud 2 = 8
o Cloud 3 = 8
o Cloud 4 = 18
Atomic Structure Practice
 If we had 7 electrons we could fill the 1st
cloud with 2 electrons.
 The remaining 5 electrons would go in the
2nd cloud.
Electron Cloud Rules
 If the outermost cloud has NOT been
completely filled, the atom/element is
considered REACTIVE.
 If the outermost cloud IS completely filled,
the atom/element is considered
UNREACTIVE.
Practice
11
P = 11
Cloud 1 = 2
Na
E = 11
Cloud 2 = 8
23.0
N = 12
Cloud 3 = 1
Drawing a Bohr Model
 Step 1: Determine Protons, Neutrons,
and Electrons
 Step 2: Draw a nucleus (about the size
of a nickel)
 Step 3: Write the Protons and Neutrons
inside the nucleus.
 Step 4: Start drawing and filling in
electron clouds with dots for electrons.
Practice
1
P=1
Cloud 1
H
E=1
**Can hold 2 Electrons
1
N=0
**Reactive
2
P=2
Cloud 1
He
E=2
**Can hold 2 Electrons
4
N=2
**Unreactive
7
P=7
Cloud 1 and 2
N
E=7
14
N = 14
**Reactive
10
P = 10
Cloud 1 and 2
Ne
E = 10
20
N = 10
**Cloud 2 can hold 8 Electrons
**Cloud 2 can hold 8 Electrons
**Unreactive