Ch. 17 – Properies of Atoms and Atomic Structure

I. Structure of the Atom Symbols

Subatomic particles Electron cloud model

A. Chemical Symbols

Capitals matter! Element symbols contain ONE capital letter

followed by lowercase letter(s) if necessary.

Co vs. COMetal that

forms bright blue solid

compounds.

Poisonous gas.

B. Subatomic Particles

POSIT IVECHARG E

PROT ONS

NEUT RALCHARG E

NEUT RONS

NUCLEUS

NEG AT IVE CHARG E

ELECT RONS

AT OM

Most of the atom’s mass. Atomic Numberequals the # of...

in a neutral atom

NUCLEUS ELECTRONS

PROTONS NEUTRONS NEGATIVE CHARGE

POSITIVE CHARGE

NEUTRAL CHARGE

ATOM

B. Subatomic Particles

Quarks

• 6 types

• 3 quarks = 1 proton or 1 neutron He

A. Orbital

Region where there is 90% probability of finding an electron.

Can’t pinpoint the location of an electron.

Density of dots represents degree of probability.

A. Orbital

Orbitals have different shapes.

B. Energy Levels

Electrons can only exist at certain energy levels.

Low energy levels are close to the nucleus.

Each energy level (n) can hold 2n2 electrons.

C. Bohr Model Diagrams

Simplified energy levels using Bohr’s idea of circular orbits.

e-

e-

Maximum e-

Level 1 2e-

Level 2 8e-

Level 3 18e-

Level 4 32e-

Lithium Atomic #: 3 Mass: 7

# of p: 3 # of e: 3 # of n: 4

p

pn

nn n

p

e-

Can replace with:

3p4n

C. Bohr Model Activity

Choose a number between 1 & 18. Find your element by the atomic number you picked. Draw a Bohr Model diagram for your element.

• Round off the mass listed on the table and subtract the atomic # to find the # of neutrons.• Abbreviate the # of ‘p’ and ‘n’ in the nucleus.

Have a partner check your drawing. Repeat with a new element.

II. Masses of Atoms Atomic Mass

Mass Number

Isotopes

A. Atomic Mass

atomic mass unit (u)

1 u = 1/12 the mass of a 12C atom

1 proton = 1 u 1 neutron = 1 u

1 u = 1.67 10-24 g

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B. Mass Number

Sum of the protons and neutrons in the nucleus of an atom.

Always a whole number.

# of neutrons = mass # - atomic #

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C. Isotopes

Atoms of the same element with different numbers of neutrons.

C126Mass #

Atomic #

Isotope symbol:

“Carbon-12”

C. Isotopes

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C. Isotopes

Average Atomic Mass• reported on Periodic Table• weighted average of all isotopes

atoms of # total

atoms) of )(## (massatoms) of )(## (mass

Avg.AtomicMass

Avg.AtomicMass

C. Isotopes

EX: About 8 out of 10 chlorine atoms are chlorine-35. Two out of 10 are chlorine-37.

atoms 10

atoms) u)(2 (37atoms) u)(8 (3535.4 u

III. The Periodic TableMendeleev

Mosely

Organization

A. Dmitri Mendeleev

Dmitri Mendeleev (1869, Russian)

• Organized elements by increasing

atomic mass.

• Predicted the existence of

undiscovered elements.

B. Henry Mosely

Henry Mosely (1913, British)

• Organized elements by increasing

atomic number.

• Fixed problems in Mendeleev’s

arrangement.

A. Metallic Character

1

2

3

4 5

6

7

Metals Nonmetals Metalloids

B. Table Sections

1

2

3

4 5

6

7

Representative Elements Transition Metals Inner Transition Metals

B. Table Sections

1

2

3

4

5

6

7

Lanthanides - part of period 6

Actinides - part of period 7

Overall Configuration

C. Columns & Rows

1

2

3

4 5

6

7

Group (Family) Period

C. Terms Valence Electrons

• e- in the outermost energy level• these determine the properties of

the elements• Elements in the same group have

the same # of valence electrons

D. Periodic Trends Group # = # of valence e- (except He)

• Families have similar reactivity Period # = # of energy levels

1A

2A 3A 4A 5A 6A 7A

8A

E. Dot Diagrams

Dots represent the valence e-. EX: Sodium

EX: Chlorine