Unit 3

Matter Organization and ChangesChapters 3, 4, and 5

Idea of the Atom

• Democritus (BC)– Had the original idea that all matter was made

of a small ‘invisible’ units– Called these atoms

• Dalton (1800’s)– Proposed his theory of matter and the atom– Widely accepted because of his evidence

Dalton’s Atomic Theory

• Every element is made of tiny, unique particles that cannot be divided

• Atoms of the same element are exactly alike

• Atoms of different elements can join to form molecules

Current Atomic Model

• Atoms can be divided– Protons

• Positive charged

– Electrons• Negative charged

– Neutrons• No charge

• Call these subatomic particles

Current Atomic Model

Nucleus

Has protons and neutrons in it

Electrons are around the nucleus

Number of Protons = Number of Electrons

Tells us the atom is neutral (no charge)

Describing the Atom

• Mass Number– Number of protons added to the number of

neutrons

protons

neutrons

9 + 9 = 18

Mass Number

• Also known as the Atomic Mass

• Can be found on the periodic table

Describing the Atom

• Atomic Number– Number of protons in the atom– Found on the periodic table

Isotopes

• Atoms of the same element that have a different number of neutrons

• Changes the mass number of the element

• Hydrogen has three isotopes– Hydrogen-1, Hydrogen-2, and Hydrogen-3

Mass number

Critical Thinking

• If Dalton were still alive, he might argue: “Atoms are neutral so they can’t be made of charged particles.” Explain why this is not true.

Periodic Table

Periods

Groups

Periodic Table Activity1. Elements in the group

2. Where the group is located on the periodic table

3. Chemical properties of the elements in the group

4. Physical properties of elements in the group

5. Types of elements in the group (metals, nonmetals, metalloids)

6. Interesting facts about the elements in the group• Each person picks one element. Need to find how

that element relates to human life. (Is it important in nutrition? Does it make something we use everyday? Etc.)

Bohr’s Addition to the Atom

• Electrons circle the nucleus like planets orbit the sun

• Electrons can only orbit in set energy levels– The further the orbit is from the nucleus, the

more energy it has

Bohr’s Atomic Model

Nucleus Energy Level 1

Energy Level 3

Energy Level 4

Energy Level 2

Bohr’s Atomic Model

• Number of electrons in the energy level furthest from the nucleus are the valence electrons

Nitrogen has seven electrons. How many valence electrons are there?

2 electrons in energy level 1

5 electrons in energy level 2 Highest energy level

Periodic Table

Happy Atoms

• Atoms are happy when they are stable

• Atoms are stable when they have a full outer energy level– Outer energy level has 8 valence electrons

Ions

• Atom that has lost or gained an electron

• Causes a change in the charge of the atom

Ions

Lithium atomCharge = neutral

Lithium ionCharge = 1+

NeutronProton

Electron

Ions

Fluorine atomCharge = neutral

Fluorine ionCharge = 1-

NeutronProton

Electron

Ions

• Chlorine – adds 1 electron

• Sodium – takes away 1 electron

• Calcium – takes away 2 electrons

• Sulfur – adds 2 electrons

• Aluminum – takes away 3 electrons

• Nitrogen – adds 3 electrons

Charge

1-

1+

2+

2-

3+

3-

Compounds

• Held together by chemical bonds– Force holding the atoms of the elements

together

• Three types of chemical bonds– Ionic– Covalent– Metallic

Structure and Properties

• The stronger the bond – the stronger the structure

• The stronger the bond – the higher the boiling point

• The stronger the bond – the higher the melting point

• The stronger the bond - the more solid the substance

Breaking Chemical Bonds

• Chemical bonds can be broken– Requires energy to break the bond

• The stronger the bond - the more energy needed to break it

• Chemical bonds are broken during chemical reactions

Forming Chemical Bonds

• Chemical bonds can be formed– Requires energy to form the bonds

• The stronger the bond - the more energy needed to form it

• Chemical bonds are formed during chemical reactions

Chemical Reactions

Na + Cl2 NaCl

Reactants Products

Chemical reactions rearrange atoms!

Reacts in the beginning Produced at the end

Chemical Reactions

• Energy is transferred during chemical reactions

• Energy exists in many forms– Light– Sound– Electricity– Heat

Reaction Rates

• How fast or slow a reaction happens is affected by– Temperature– Pressure– Surface area– Concentration– Size and shape– Catalyst

Reaction Rates

• Temperature– Increase temperature = increase reaction rate– Potato cooks faster in hot water than cold

• Pressure– Increase pressure = increase reaction rate– Coal burns faster at higher pressure

• Surface area– Increase surface area = increase reaction rate– Cut potato cooks faster than uncut

Reaction Rates

• Concentration– Higher concentration = increase reaction rate– More bleach causes lighter color

• Size and shape– Smaller size = increase reaction rate– Large piece of zinc reacts slower than a small

• Catalyst – If it is present = increase reaction rate– Add protease to digest protein