1. Elements and Compounds Atomic Theory

2. Elements, Compounds, and Mixtures
Matter can be broadly classified into 3 types
Mixtures
Compounds
Elements

3. How do Different kinds of molecules differ?
Nearly all matter (molecules) we encounter in life is a mixture of substances.
Mixture = blend of 2 or more substances
Air = mixture of gases
Tap water = minerals and gases

4. What happens when a mixture is separated?
When components of mixture are separated, they are separated into pure substances.
Pure substance =constant properties and constant composition
Example: Salt water = salt + water

5. Can pure substances be divided into different categories?
Pure substances can be divided into 2 categories: compound or element

6. Elements and Compounds
Element = simplest type of matter with unique physical and chemical properties.
Element consists of only one kind of atom
Compound =type of matter composed of two or more different elements that are chemically bound together.

7. Defining the Atom
An atom is the smallest particle of an element that retains its identity in a chemical reaction.

8. Dalton’s Atomic Theory
All elements are composed of tiny particles called atoms.
Atoms of the same element are identical.
3. Atoms of different elements can physically mix in simple whole number ratios to form compounds.
4. Chemical reactions occur when atoms are separated, joined, or rearranged.

9. How do we represent atoms?
We draw circle pictures!!!
Dalton drew circle pictures to represent each kind of atom.
Element A
Element B
Mixture of A & B
Compound of A & B
Another Compound of A & B

10. Atom & Molecule Cartoons
What’s in the box?
Individual atoms, or molecules?
Substance (pure) or mixture?
Compound, element, or both?

11. Atom & Molecule Cartoons
What’s in the box?
Individual atoms, or molecules?
Substance (pure) or mixture?
Compound, element, or both?

12. Atom & Molecule Cartoons
What’s in the box?
Individual atoms, or molecules?
Substance (pure) or mixture?
Compound, element?

13. The Nuclear Model of the Atom
Rutherford proposed:
The atom’s mass is concentrated in a tiny positive nucleus
Lightweight negative electrons circle the nucleus as planets orbit the sun
Most of the atom is empty space

14. Atomic Composition Atoms are made up of subatomic particles: Particle
Charge
Location
Mass
Electron (e-)
Negative (-)
Outside nucleus
9.109 x 10–28 g
Proton (p+)
Positive (+)
Inside nucleus
1.673 x 10–24 g
Neutron (n0)
No charge
1.675 x 10–24 g

15. Structure of Atom
Most of the volume in an atom is occupied by electrons.
2. The nucleus is the central core of an atom and it is composed of protons and neutrons.

16. Distinguishing Between Atoms
The number of protons present in an atom determines which atom you have.
Protons = atomic number.
The mass # of an atom is determined by the number of protons and neutrons.
Mass # = protons + neutrons
Neutrons = mass – protons
Not all elements are the same.
Isotopes =same element with a different # of neutrons
This is called the weighted mass average.
This system of mass based on the mass of Carbon-12.

17. Atomic composition 23 11 Na1+
mass number, A
protons + neutrons 
atomic number, Z 
protons
 ion charge
protons – electrons
Atomic number is found on the periodic table
Mass number is NOT found on the periodic table
An atom may gain/lose electrons to form an ion
If no charge is shown, the charge is zero (a neutral atom)

18. Let’s practice Symbol Protons Neutrons Electrons Atomic # Mass # 12 C21

19. Isotopes Both are the element lithium 6Li has 3 protons, 3 neutrons
Atoms with the same number of protons but different numbers of neutrons are isotopes of the same element
6Li and 7Li are isotopes of lithium
Both are the element lithium
6Li has 3 protons, 3 neutrons
7Li has 3 protons, 4 neutrons
Their chemical behaviors are identical

20. Let’s Practice
Oxygen has three naturally-occurring isotopes, with 8, 9, and 10 neutrons. Write the symbols for each of the isotopes.