Combinations of Atoms

Chapter 4.2Page 87

Organization of the Periodic Table

Each Box gives information about one element Name of element Atomic number

(number of protons)

Atomic Symbol Atomic Mass

Position shows electron arrangement

Periods—horizontal rows

Give number of electron shells used

Groups Groups—vertical

columns Within a column

elements have the same number of valence electrons

Atoms are the building blocks of molecules

Molecules The smallest unit of matter that

can exist by itself and retain all of a substances chemical properties

In a molecule two or more atoms are bonded together

Diatomic molecules di--two Some molecules are made of the

same kind of atom

O2

Ozone is O3

Chemical Formulas A combination of letters and

numbers that shows the number of atoms of each element that are required to make a molecule of the compound

Chemical Equations Elements and compounds often

combine through chemical reactions

The reaction can be described in a formula

Photosynthesis formula

6H2O + 6CO2 -------> C6H12O6+ 6O2

Reactants on left products on right

The arrow is read yields

Balanced equations

An equation is balanced when the number of atoms on the right equals the number of atoms of the same element on the left

To balance a formula you use coefficients

Photosynthesis formula

6H2O + 6CO2 -------> C6H12O6+ 6O2

What is the blue arrow pointing to?What is the red arrow pointing to?

CO2

H2O

Book example Magnesium, Mg, reacts with oxygen, O2, to

form MgO, magnesium oxide

Write a balanced equation. We have two oxygen on the right so we will

need a number 2 on the left as a coefficient

2 Mg + O2 2MgO

Chemical Bonds The forces that hold together the atoms

in molecules are called

chemical bondsBonds form because of attraction

between opposite charges

Atoms can share or transfer valence electrons

Ions When an electron

is transferred from one atoms to another both atoms become charged

A charged particle like an atom or

molecule is an ion

Cat lover or cat hater

A positively charged ion is a cation (+)

A negatively charged ion is called an anion (-)

Ionic Bonds Attractive force

between two oppositely charged ions that result from the transfer of electrons from one atom to another is called

An ionic bond

Na from the left wants to give away

Cl from the right wants to gain electrons

Ionic bonds form from atoms from opposite sides of the periodic table

Covalent Bonds A bond between

atoms that share electrons is called a

covalent bond

http://www.ithacasciencezone.com/chemzone/lessons/03bonding/mleebonding/covalent_bonds.htm

Polar Covalent Bonds Some atoms that are

covalently bonded do not equally share elections

A covalent bond with unequal attraction is called a polar covalent bond

Water is one example

Metallic Bonds Electrons flow

easily They are not

tightly bound

This explains the properties of metals

Electron From Greek word for amber Ben Franklin found electricity

was a flow of electrons

Ben Franklin found electricity is the flow of electrons

Physical Change

A change of matter from one form to another without a change in chemical properties Break Crush Melt

140

Change of State is a physical change An item can

change from solid to liquid to gas and still have the same chemical formula

140

Dissolving is a physical change

Example: dissolve salt in water You still have salt and water You could evaporate the water and get the salt back

Something that dissolves is soluble 140

Chemical Changes Form new substances with different

physical properties Can be detected

Fizz Smell Color Produce heat Produce a sound

Cannot be reversed by physical means

142

Exothermic—produce heat Endothermic—solution gets colder

Mixtures A combination of two or more

substances that are not chemically combined

Two types: Heterogeneous--different Homogenous--same

Heterogeneous mixtures Two or more substances are

not uniformly distributed

Example Granite

Homogenous mixture Having the

same composition throughout

Solution A homogenous

mixture of two or more substances that are uniformly dispersed

When a substance dissolves it goes into solution

Example salt in water

Compounds can be broken down by physical means

Carbonic acid in pop gives it fizz When the bottle is opened the

acid breaks down into carbon dioxide and water

Carbon dioxide escapes as bubbles

Mixtures can be physically separated

By Density Solubility Magnetism

Lab Activity Design an experiment to separate the

mixture in your sample—list the steps you will take below

Be sure to clean up your area when you are through

141

Test for the presence of CO2 and H2

A flaming splint is used to detect the presence of carbon dioxide or hydrogen gas CO2 extinguishes the flame H2

Creates a hydrogen burp

142