Modern Atomic Theory

Modern Atomic Theory

Bohr Model of the Atom

The Bohr model of the atom

• Proposed in 1913

• Atoms are like tiny solar systems according to this model.

• Electrons are in set orbits because of their energy

• Electrons in an atom can move from one energy level to another

• Electrons move up when an atom absorbs energy

• An atom gives off energy when an electron moves to a lower energy level

Multiple Choice

The Bohr model is often compared to

• a marble

• an onion

• plum pudding

• a solar system

• bowling ball

Because of Bohr's work, we have developed the electron cloud model.

Electron Cloud Model

• Electrons move in rapid, random motion and give a "cloudlike" appearance, like the blades of a fast moving fan.

• Electrons are found in regions of high probability called orbitals.

Multiple Choice

Where in the electron cloud are electrons probably found?

• straight lines

• orbitals

• little circles

• taco time

• inside the nucleus

Electron Cloud Model continued...

• The bigger the atom, the more orbitals it may contain for electrons

• Each orbital may hold a maximum of two electrons

• Each energy level holds a different number of orbitals.

Multiple Choice

How many electrons can each orbital hold?

• 1

• up to 2

• up to 8

• up to 18

• As many as you want

Orbitals and electrons in the first four energy levels

• The first energy level can hold 1 orbital and 2 electrons

• The second energy level can hold 4 orbitals and 8 electrons

• The third energy level can hold 9 orbitals and 18 electrons

• The 4th energy level can have 16 orbitals and 32 electrons

Multiple Choice

What is the maximum number of electrons in the 3rd energy level?

• 2

• 8

• 18

• 32

• 1.5

Electron Wrap up

• Electrons are found in areas of the atom called energy levels.

• In each energy level, there are regions of high probability of finding electrons. These are called orbitals.

• You can only have up to two electrons in each orbital.

• The arrangement of electrons in the electron cloud is called the electron configuration.

• 1st level 2 electrons, 2nd level 8 electrons, 3rd level 18 electrons, 4th level 32 electrons

Periodic table of the elements

• Demitri Mendeleev - Russian Chemist and Teacher

• Liked Solitaire and arranged the elements into columns based on atomic mass (modern table is arranged by atomic number)

• Vertical columns on the table are called GROUPS

• Horizontal Rows on the table are called PERIODS

Multiple Choice

Mendeleev was from what country

• Poland

• Germany

• Australia

• Russia

• Italy

Valence electrons

• A Valence Electron is an electron that is the outermost (highest) occupied energy level of an atom.

• Valence electrons are the only electrons that interact during chemical reactions and bonding.

• Elements in a group have similar properties because they have the same number of valence electrons.

• For example all elements in 3A have 3 valence electrons and all elements in 7 A have 7 valence electrons.

Groups and their Valence Electrons

• Group 1A (Alkali Metals) - 1 valence electron

• Group 2A (Alkaline Earth Metals) - 2 valence electrons

• Group 3A - 3 valence electrons

• Group 4A - 4 valence electrons

• Group 5A - 5 valence electrons

• Group 6A - 6 valence electrons

• Group 7A (Halogens) - 7 valence electrons

Groups and their Valence Electrons cont...

• Group 8A (noble gases) - 8 valence electrons

• Atoms WANT to end up with 8 electrons in their outer energy level because that is how they become the most stable (most happy)

Multiple Choice

How many valence electrons does Magnesium (Mg) have?

• 1

• 2

• 3

• 5

• 7

Multiple Choice

How many valence electrons does Neon (Ne) have?

• 2

• 4

• 6

• 8

• 1

Multiple Choice

How many valence electrons does Sulfur (S) have?

• 3

• 5

• 6

• 7

• 2

Multiple Choice

How many valence electrons does Aluminum (Al) have?

• 7

• 6

• 5

• 4

• 3

Multiple Choice

How many valence electrons does Carbon (C) have?

• 1

• 5

• 3

• 6

• 4

Multiple Choice

How many valence electrons does Helium (He) have?

• 2

• 4

• 6

• 8

Multiple Choice

Which group is known as the Alkaline Earth Metals?

• Group 1A

• Group 2A

• Group 7A

• Group 8A

Multiple Choice

Which group is known as the Halogens?

• Group 1A

• Group 2A

• Group 7A

• Group 8A

Multiple Choice

Which group does not react with any other elements?

• Alkali Metals

• Alkaline Earth Metals

• Halogens

• Noble Gases

IONS

• Because atoms are more stable with a full valence shell (outer energy level), they will often times give up or gain electrons

• Any atom that gains or loses electrons is called an ION

• An atom that gains electrons is called an anion and has a negative charge (it has more electrons (-) than protons (+))

• An atom that loses electrons is called a cation and has a positive charge (it has more protons(+) than electrons(-))

Multiple Choice

An atom that has lost an electron is called a(n)

• anion

• cation

• isotope

• nucleus

Multiple Choice

an atom that has gained an electron is called a(n)

• anion

• cation

• isotope

• nucleus

Multiple Choice

What is the charge on a potassium (K) ion?

• 1+

• 2+

• 1-

• 2-

Multiple Choice

What is the charge on an Oxygen ion?

• 1+

• 2+

• 1-

• 2-

Multiple Choice

What is the charge on a Bromine ion?

• 1+

• 2+

• 1-

• 2-

Multiple Choice

What is the charge on an Aluminum ion?

• 4 +/-

• 2+

• 3+

• 3-

• 2-