Review

• Scientist who discovered the electron using the cathode ray tube

–Thomson• Scientist who used the oil drop experiment to

discover the charge on the electron

–Millikan• Scientist who conducted the gold foil

experiment to discover that the nucleus is small, dense, and positively charged.

–Rutherford

Review

• Scientist that developed the pulsating planetary model

–Bohr• Scientist that discovered the existence of the

neutron

–Chadwick• Scientist that had the solid sphere model of

the atom

–Dalton

Review

• Greek philosopher who coined the term atom from the Greek word atomos

–Democritus• Greek philosopher who did not believe in the

atom

–Aristotle• Scientist who created the law of definite

proportions

–Proust

Review

• Scientist who created the law of multiple proportions

–Dalton• Scientist who created the law of conservation

of mass

–Lavoisier

Review

• An An atomatom is the smallest particle of an is the smallest particle of an element that gives it its chemical and element that gives it its chemical and physical properties.physical properties.

• The atom is extremely small. One teaspoon The atom is extremely small. One teaspoon of water has 3 times as many atoms as the of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water.Atlantic Ocean has teaspoons of water.

• If a large sports stadium were an atom, a If a large sports stadium were an atom, a marble would represent the nucleus.marble would represent the nucleus.

An atom consists of aAn atom consists of a

• Positively Positively charged nucleus that contains charged nucleus that contains protonsprotons and and neutronsneutrons

• Negatively Negatively chargedcharged electrons electrons in space outside in space outside of the nucleus.of the nucleus.

Atom Atom StructureStructure

NucleusNucleus

Electron cloudElectron cloud

Atoms found in nature have a neutral charge.

Why?

Atomic NumberAtomic Number

All atoms of the same element All atoms of the same element have the same number of have the same number of protons in the nucleusprotons in the nucleus

1313

AlAl

26.98126.981

Atomic numberAtomic number

Atom symbolAtom symbol

AVERAGE Atomic MassAVERAGE Atomic Mass

Atomic NumberAtomic Number

Atomic # = # protons =

# electrons

*only for neutral atoms

Mass NumberMass Number

• Mass NumberMass Number

= # protons + # neutrons= # protons + # neutrons

• NOT on the periodic table, NOT on the periodic table, electron is so small that its mass is electron is so small that its mass is negligiblenegligible

Average Atomic Mass

•Weighted average, more abundant isotopes have a greater affect

–On the periodic table

Atomic Symbols

Hyphen/mass notation - show the name of the

element, a hyphen, and the mass number in

sodium-23

Nuclear symbol - show the mass number and atomic

number next to the chemical symbol

mass number 23 Na

atomic number 11

Figure 3.10: Two isotopes of sodium.

IsotopesIsotopes

• Atoms of the Atoms of the same element same element but but different different mass numbermass number..

• Boron-10 (Boron-10 (1010B) has 5 p and 5 nB) has 5 p and 5 n

• Boron-11 (Boron-11 (1111B) has 5 p and 6 nB) has 5 p and 6 n

10B

11B

Practice

•Ar-40

•P-31

Isotopes?

Which of the following represent isotopes of the same element? Which element?

234 X 234

X235

X238

X

92 93 92 92

1.1. An An __ _____ ___ is the smallest particle of is the smallest particle of an element that has the chemical properties an element that has the chemical properties of the element.of the element.

2. The 3 particles that make up the atom 2. The 3 particles that make up the atom are are ________________, , __________________, and , and __________________..

3. Atoms with the same number of protons 3. Atoms with the same number of protons and electrons, but a different number of and electrons, but a different number of neutrons are called neutrons are called ________________________..

4. 4. ______________________ was an English scientist was an English scientist who developed an atomic theory in the who developed an atomic theory in the early 1800s. early 1800s.