Outline the history of the atomic model.

Agenda for Tuesday Dec 14th 1. Atoms2. Atomic mass, #, protons, etc

Atoms

• Nucleus in the center– Protons and neutrons

• Electrons on outside of nucleus– Electron cloud model– Electrons exist in energy levels – based on # of

electrons

Atomic Number and Atomic Mass

Bboron

5

10.811

Element nameAtomic number

Symbol

Atomic mass

• Atomic number: # of protons in nucleus

• Each element has a different atomic #

• Identifies the element

• Hydrogen = smallest atomic # (1)

• # of protons = # of electrons

• Atomic mass: total mass of protons and neutrons in an atom, measured in atomic mass units (amu)– Atomic weight

• Atoms of the same element can have different numbers of neutrons - isotopes

• # on periodic table is the average atomic mass for that element

• We will round the average atomic mass to get a whole # called the mass number.

• Examples:Sodium (Na)

Avg. atomic mass = 22.990 amuMass # = 23

Nitrogen (N)Avg. atomic mass = 14.007 amuMass # = 14

• Finding # of neutrons

mass # - atomic # = # of neutrons

For Na: 23 – 11 = 12 neutrons

For N:14 – 7 = 7 neutrons

Practice

Find the mass number, protons, neutrons, and electrons for Bromine.

Agenda for Wednesday Dec 15th 1. History of the Atom Flash Cards2. Practice with mass, protons, etc3. Isotopes

ElementName

AtomicNumber

Number ofProtons

Number ofNeutrons Mass Number

carbon 12

8 8

hydrogen 1

6 14

hydrogen 2

nitrogen 14

6 66

7 7 7

1 1 3

86

1 01

168Oxygen

Carbon

Isotopes• Atoms of the same element can have different numbers of

neutrons isotopes

• # of protons and electrons stays the same for a particular element– Mass changes– Means # of neutrons changes

• Atomic mass on your P.T. is an average of all the isotopes

• For Boron:.8 (10 amu) + .2 (11 amu) = 10.811 amu

More on Isotopes

• Because the numbers of neutrons in the isotopes are different, the mass numbers are also different

• You use the name of the element followed by the mass number of the isotope to identify each isotope: boron-10 and boron-11

• Example: – Neon. All neon atoms have 10 protons and 10

electrons. Some neon atoms have 10 neutrons and some have 12.

– Both isotopes of neon

Ne or Ne-20

Ne or Ne-22

10

10

20

22

Atomic # (# of protons)

Atomic # (# of protons)

Mass # (protons + neutrons). Different for each isotope

Mass # (protons + neutrons). Different for each isotope

What’s the point of Isotopes

• You can tell how old something is– Radiocarbon Dating

• Use as markers in research– Follow a certain molecule, atom

Practice ProblemsYou will need your periodic table!

1. For Mg-25: How many protons, electrons, and neutrons?

2. For N-15: How many protons, electrons, neutrons?

3. For P-31: How many protons, electrons, neutrons?

Practice

What is an isotope?

Agenda for Thursday Dec 16th 1. Mass #, Atomic weight, proton review2. Valence Electrons3. Lewis Dot Structures

Atoms

• Nucleus in the center– Protons and neutrons

• Electrons on outside of nucleus– Electron cloud model– Electrons exist in energy levels – based on # of

electrons

Valence Electrons

• Electrons in the outermost energy level

• Valence electrons determine reactivity and other chemical properties

• 8 valence electrons means a stable atom = do not want to react with other atoms

Where are electrons found?NucleusLeast likely

Most likely

13 p+

14 n0

Help! We’re so

vulnerable!

Valence electrons

•A way to draw an atom showing where electrons are found

Valence electrons

Carbon -12 has 4 electrons in the last energy level . . .

therefore carbon-12 has 4 valence electrons

Bohr’s Model

Nucleus

1st shell can hold 2 e-

3rd shell can hold 8 e-

2nd shell can hold 8 e-

How many electrons in each shell?

• 1st shell = 2 electrons• 2nd shell = 8 electrons• 3rd shell = 8 electrons• 4th shell = 18 electrons

Drawing Carbon-12 with Bohr’s ModelSteps:1. Find number

of neutrons and protons.

2. Find number of electrons.

3. Fill in electrons, beginning with the 1st energy level.

How many valence electrons does Nitrogen have?

NUCLEUS

How many valence electrons does Calcium have?

Calcium has 2 Valence electrons

NUCLEUS

How many valence electrons does Phosphorous have?

Phosphorous has 5 Valence electrons

NUCLEUS

How many valence electrons does Boron have?

NUCLEUS

Boron has 3 Valence electrons

Cool Trick!

162 3 4 5 7

8