CHAPTER 4

Atomic Structure

Atoms

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

History

Democritus (460-370BC): first suggested the existence of the atom

History

John Dalton (1766-1844): proposed the Atomic Theory: 1. All elements are made of atoms 2. Atoms of the same element are identical 3. Atoms of different elements can combine

to form compounds 4. Chemical reactions occur when atoms are

separated, joined, or rearranged

Size of the atom

One penny contains 2.4x1022 atoms of copper100,000,000 atoms in a row would be 1 cm

longAtoms can be seen with special microscopes

called scanning tunneling microscopes

Atomic Structure

An atom can be broken down into subatomic particles: protons, neutrons, and electrons.

Parts of an atom

The nucleus is the tiny central core of an atom containing protons and neutrons

Surrounding the nucleus is the electron field where electrons are located.

If an atom was the size of a football field, the nucleus would be the size of a marble located on the 50 yard line.

Subatomic Particles

Particle Symbol Location Charge Mass (g)

Electron e- orbital - 9.11 x 10-

28

Proton p+ nucleus + 1.67 x 10-

24

Neutron n0 nucleus 0 1.67 x 10-

24

Protons

Protons are positively charged subatomic particles located in the nucleus

Neutrons

Neutrons are subatomic particles with no charge, equal in size to protons, and found in the nucleus.

Electrons

Electrons are negatively charged subatomic particles, which are very small, and orbit the nucleus.

Important Scientists

J.J. Thomson (1897) discovered electrons using a cathode ray tube.

Cathode Ray Experiment

Important Scientists

Ernest Rutherford (1911) discovered protons through his gold foil experiment.

Gold Foil Experiment Animation

Reading and Writing in Science

1. Read pages 100-108 in the red textbook

2. Answer questions 1-14 on pages 103 and 108. Write and answer these questions in your notebooks.

Next notebook collection date is October 30.

Distinguishing Among Atoms

Atoms of an element are different because they contain different numbers of protons.

The atomic number of an element is the number of protons an atom of that element has.

Practice

How many protons does each element have?

Hydrogen CarbonNitrogenPotassiumGold

Practice

How many protons does each element have?

Hydrogen = 1 Carbon = 6Nitrogen = 7Potassium = 19Gold = 79

Mass Number

The other number on the periodic table is an atom’s mass number which is the sum of protons and neutrons.

What is the mass number of:Hydrogen Carbon NitrogenPotassiumGold

Mass Number

The other number on the periodic table is an atom’s mass number which is the sum of protons and neutrons.

What is the mass number of:Hydrogen (1.0079) Carbon (12.011)Nitrogen (14.007)Potassium (39.098)Gold (196.97)

Neutrons

To determine the number of neutrons an atom has, you subtract the atomic number from the mass number, then round to the nearest whole number.

How many neutrons are found in:HydrogenCarbonNitrogenPotassiumGold

Neutrons

To determine the number of neutrons an atom has, you subtract the atomic number from the mass number, then round to the nearest whole number.

How many neutrons are found in:Hydrogen = 0Carbon = 6Nitrogen = 7Potassium = 20Gold = 118

Electrons

In a neutral atom, the number of electrons is equal to the number of protons, which is equal to the atomic number.

How many electrons does each atom have?HydrogenCarbonNitrogenPotassiumGold

Electrons

In a neutral atom, the number of electrons is equal to the number of protons, which is equal to the atomic number.

How many electrons does each atom have?Hydrogen = 1Carbon = 6Nitrogen = 7Potassium = 19Gold =79

Determining subatomic particles

Particle Number

Protons Atomic Number

Electrons

Atomic Number

Neutrons

Atomic mass – atomic number

Isotopes

Isotopes are atoms that have the same number of protons but different numbers of neutrons (and therefore different mass numbers).

Isotopes

The most well known isotope is Carbon-14. Regular Carbon is called Carbon-12, because

its mass number is 12, and it has 6 neutrons.Carbon 14 has 8 neutrons (14-6).It is used for radioactive dating of fossils.

Getting to know the Periodic Table

You should memorize the names and symbols of common elements on the periodic table.

Complete the activity to help you get to know the elements of the periodic table.

History of Atomic Models

Over time, scientists proposed different models of atoms, each better than the last.

Rutherford said that positive protons were in the nucleus, and electrons orbited it.

Atomic Models

Bohr stated that the nucleus had positive protons, and electrons orbited in fixed shells.

Atomic Models

Schrodinger proposed the quantum mechanical model, which is still used today.

It states that there are protons and neutrons in the nucleus, which is surrounded by an electron cloud showing the probability of electron location.

Electrons

Electrons are found outside the nucleus in shells/orbitals/energy levels.

Energy Levels

The number of electrons allowed in each energy level is:

Energy Level (n) Maximum Number of Electrons

1 2

2 8

3 18

4 32

Placing electrons

Each energy level must be full before electrons can be placed in the next level up.

Example: Draw an atom of Lithium

Lithium

Practice

Draw an atom of Sodium.

Sodium

Practice

In your notebooks, draw the first 30 atoms. Name each one, and place the correct numbers of protons, neutrons, and electrons in each.

This is what your quiz will be like (Tuesday for periods 5 and 7, Wednesday for period 2)