The Atom Atomic Number and Mass Number Isotopes. Three fundamental parts of an atom are: protons electrons neutrons Structure of the atom is: protons

The Atom

Atomic Number and Mass Number

Isotopes

Three fundamental parts of an atom are:

protons electrons neutrons

Structure of the atom is:

protons and neutrons are found in the nucleus electrons are located outside of the nucleus

Atomic Theory

Atoms are building blocks of elements

Similar atoms in each element

Different from atoms of other elements

Two or more different atoms bond in simple

ratios to form compounds

Subatomic Particles

There are three subatomic particles that are of

interest to chemists. These particles define the

nature of atoms and how they are put together.

These particles are:

• Neutrons

• Protons

• Electrons

Properties of Subatomic Particles

Particle Mass, gRelative mass to

C-12, amu

Charge, Coulombs

Unit Charge

proton 1.6726 x 10-24 1.00728 1.67 x 10-19 +1

electron 9.1096 x 10-28 0.000549 -1.67 x 10-19 -1

neutron 1.6749x 10-24 1.00867 0 0

Subatomic Particles

Particle Symbol Charge RelativeMass

Electron e- 1- 0

Proton p+ + 1

Neutron n 0 1

Location of Subatomic Particles

10-13 cm

electrons

protons

neutrons

10-8 cm

nucleus

Representation of Atoms

XAZElementSymbol

Mass Number

Atomic Numbe

r

Atomic Number

Counts the number

of

protons

in an atom

Periodic Table

Represents physical and chemical

behavior of elements

Arranges elements by increasing atomic

number

Repeats similar properties in columns

known as chemical families or groups

Periodic Table

1 2 3 4 5 6 7 8

11 Na

Atomic Number on the Periodic Table

11

Na

Atomic Number

Symbol

All atoms of an element have the same number of protons

11

Na

11 protons

Sodium

Counting Protons

State the number of protons for atoms of each of the following:

A. Nitrogen

1) 5 protons 2) 7 protons 3) 14 protons

B. Sulfur


C. Barium


Solution

State the number of protons for atoms of each of the following:

A. Nitrogen

2) 7 protons

B. Sulfur

2) 16 protons

C. Barium

3) 56 protons

Number of Electrons

An atom is neutral The net charge is zeroNumber of protons = Number of electronsAtomic number = Number of electrons

Mass Number

Counts the number

of

protons and neutrons

in an atom

Atomic Symbols

Show the mass number and atomic number

Give the symbol of the element

mass number

23 Na sodium-23

atomic number 11

More Atomic Symbols

16 31 65

O P Zn

8 15 30

8 p+ 15 p+ 30 p+

8 n 16 n 35 n8 e- 15 e- 30 e-

Isotopes

Atoms with the same number of protons,

but different numbers of neutrons.

Atoms of the same element (same atomic

number) with different mass numbers

Isotopes of chlorine

35Cl 37Cl17 17

chlorine - 35 chlorine - 37

Counting Protons, Neutrons & Electrons

Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.

12C 13C 14C 6 6 6

#P _______ _______ _______

#N _______ _______ _______

#E _______ _______ _______

Solution

12C 13C 14C 6 6 6

#P __6___ _ 6___ ___6___

#N __6___ _ _7___ ___8___

#E __6___ _ 6___ ___6___

Protons, Neutrons & Electrons

An atom of zinc has a mass number of 65.

A. Number of protons in the zinc atom

1) 30 2) 35 3) 65

B. Number of neutrons in the zinc atom

1) 30 2) 35 3) 65

C. What is the mass number of a zinc isotope

with 37 neutrons?

1) 37 2) 65 3) 67

Solution

An atom of zinc has a mass number of 65.

A. Number of protons in the zinc atom

1) 30

B. Number of neutrons in the zinc atom

2) 35

C. What is the mass number of a zinc isotope

with 37 neutrons?

3) 67

Atomic Symbols

Write the atomic symbols for atoms with the following:

A. 8 p+, 8 n, 8 e- ___________

B. 17p+, 20n, 17e- ___________

C. 47p+, 60 n, 47 e- ___________

Solution

16OA. 8 p+, 8 n, 8 e- 8

B. 17p+, 20n, 17e- 37Cl 17

C. 47p+, 60 n, 47 e- 107Ag 47

Identifying Elements

An atom has 14 protons and 20 neutrons.A. Its atomic number is

1) 14 2) 16 3) 34

B. Its mass number is1) 14 2) 16 3) 34

C. The element is1) Si 2) Ca 3) Se

D. Another isotope of this element is

1) 34X 2) 34X 3) 36X 16 14 14

Solution

An atom has 14 protons and 20 neutrons.A. It has atomic number

1) 14

B. It has a mass number of3) 34

C. The element is1) Si

D. Another isotope of this element would be

3) 36X 14

Masses of Atoms

A scale designed for atoms gives their small

atomic masses in atomic mass units (amu)

An atom of 12C was assigned an exact mass of

12.00 amu

Relative masses of all other atoms was

determined by comparing each to the mass of 12C

An atom twice as heavy has a mass of 24.00

amu. An atom half as heavy is 6.00 amu.

Atomic Mass

Listed on the periodic table

Gives the mass of “average” atom of each

element compared to 12C

Average atom based on all the isotopes and their

abundance %

Atomic mass is not a whole number

Na22.99

Atomic Mass

Using the periodic table, specify the atomic mass of each element (round to the tenths place):

A. calcium __________

B. aluminum __________

C. lead __________

D. barium __________

E. iron __________

Solution

Using the periodic table, specify the atomic mass of each element (round to the tenths place):

A. calcium _40.1 amu _

B. aluminum _27.0 amu _

C. lead _207.2 amu_

D. barium _137.3 amu_

E. iron _55.8 amu__

Calculating Atomic Mass

Percent(%) abundance of isotopes

Mass of each isotope of that element

Weighted average =

mass isotope1(%) + mass isotope2(%) + …

100 100

Atomic Mass of Magnesium

Isotopes Mass of Isotope Abundance 24Mg = 24.0 amu 78.70%

25Mg = 25.0 amu 10.13%

26Mg = 26.0 amu 11.17%

Atomic mass (average mass) Mg = 24.3 amu

Mg24.3

CalculatingAtomic Mass

Gallium is a metallic element found in

small lasers used in compact disc players.

In a sample of gallium, there is 60.2% of

gallium-69 (68.9 amu) atoms and 39.8% of

gallium-71 (70.9 amu) atoms. What is the

atomic mass of gallium?

Solution

Ga-69

68.9 amu x 60.2 = 41.5 amu for 69Ga

100

Ga-71 (%/100)

70.9 amu x 39.8 = 28.2 amu for 71Ga

100

Atomic mass Ga = 69.7 amu

Finding An Isotopic Mass

A sample of boron consists of 10B (mass 10.0 amu) and 11B (mass 11.0 amu). If the average atomic mass of B is 10.8 amu, what is the % abundance of each boron isotope?

Assign X and Y values:X = % 10B Y = % 11B

Determine Y in terms of XX + Y = 100Y = 100 - X

Solve for X:X (10.0) + (100 - X )(11.0) = 10.8

100 100

Multiply through by 10010.0 X + 1100 - 11.0X = 1080

Collect X terms

10.0 X - 11.0 X = 1080 - 1100

- 1.0 X = -20

X = -20 = 20 % 10B

- 1.0

Y = 100 - X

% 11B = 100 - 20% = 80% 11B

Isotopes of Copper

Copper has two isotopes 63Cu (62.9 amu) and 65Cu (64.9 amu). What is the % abundance of each isotope? (Hint: Check periodic table for atomic mass)

1) 30% 2) 70% 3) 100%

Solution

2) 70%

Solution

62.9X + 6490 = 64.9X = 6350

-2.0 X = -140

X = 70%

Isotopes of chlorine

Naturally occurring chlorine consists of 75.53% of the isotope with mass number 35 and 24.47% of the isotope with mass number 37. What is the average atomic mass of naturally occurring chlorine?

electronsneutronsprotonsCl

electronsneutronsprotonsCl

172017

171817

3717

3517

Solution

(0.7553)(34.97 u) = 26.41 u(0.2447)(36.95 u) = 9.04 u

Atomic mass of Cl = 35.45 u

Where Are the Electrons Located?

This question becomes important since the nuclear model of the atom proposed by Rutherford accounted only for the location of the positively charged particles. The location of the electrons is the key to understanding chemistry.

Documents

The Atom Atomic Number and Mass Number Isotopes. Three fundamental parts of an atom are: protons electrons neutrons Structure of the atom is: protons