1. Chapter 2 “Matter is made up of atoms”

2. Greeks
Proposed that matter was made up of four elements (air, water, earth, & fire)
Did not test their hypotheses

3. Democritus
Proposed that the world is made up of empty space and tiny particles called atoms
Thought that atoms were the smallest particles of matter and that different types of atoms exist for every type of matter

4. Antoine Lavoisier
Made measurements of chemical changes in a sealed container
Observed that the mass of reactants before a chemical reaction was equal to the mass of products after reaction
conclusions became known as law of conservation of mass

5. Joseph Proust
observed that the composition of water is always 11 % hydrogen and 89 % oxygen by mass, regardless of source
observed other compounds and noticed that the elements that made up compound was always in a certain proportion by mass
principle referred to as law of definite proportions

6. John Dalton Proposed his atomic theory in 1803 which states:
all matter is made up of atoms
atoms are indestructible and cannot be divided into smaller particles
all atoms of one element are exactly alike, but they are different from atoms of other elements

7. Atomic Structure Subatomic Particles Particle Symbol Charge
Particle
Symbol
Charge
Mass in Grams
Proton p+ +1
1.67 X 10-24
Neutron n0
Electron e- -1
9.11 X 10-28

8. Periodic Table Block Cl (c) Chlorine (a) 17 (b) (a) Element name
(b) Atomic number
( c ) Element symbol
(d) Atomic mass

9. # neutrons = mass # - atomic # (chlorine has 18 neutrons)
Atomic number = # of protons (chlorine has 17 protons)
Mass number is the rounded atomic mass (mass number of chlorine is 35)
# neutrons = mass # - atomic # (chlorine has 18 neutrons)
# electrons = atomic # (for neutral atoms)

10. Isotopes
atoms of the same element that differ in mass and number of neutrons (they have the same number of protons)
identified by writing the name or symbol of element followed by its mass number (Cl-37 or chlorine-37)

11. The Electron Cloud Model
Energy levels are spherical regions of space around the nucleus in which electrons are most likely found
Electron cloud is the space around the nucleus of an atom where the atom’s electrons are found

12. Energy Levels Can hold a limited number of electrons
Lowest energy level is the smallest and closet to the nucleus
The farther from the nucleus the larger the energy level

13. Energy Levels (cont’d)
1st energy level can hold 2 electrons
2nd energy level can hold 8 electrons
3rd energy level can hold 18 electons

14. Energy Levels (cont’d)
Electrons in outermost energy level are called valence electrons

15. Lewis Dot Diagrams
Illustrates valence electrons as dots around the chemical symbol of an element
Each dot represents one valence electron
Symbol represents the core of the atom