CHEM 101 Ch. 4 Atoms and Elements

Question 0

Describe Rutherford’s gold foil experiment and the results of the experiment. How did these results contradict the plum pudding model of the atom?

Answer 0

Rutherford’s gold foil experiment involved sending positively charged alpha particles through a thin sheet of gold foil and detecting if there was any deflection of the particles. He found that most passed straight through, yet some particles showed some deflection. This result contradicts the plum pudding model of the atom because the plum pudding model does not explain the deflection of the alpha particles.

Question 1

What did Democritus contribute to our modern understanding of matter?

Answer 1

Democritus theorized that matter was ultimately composed of small, indivisible particles called atoms. Upon dividing matter, one would find tiny, indestructible atoms.

Question 2

List the three subatomic particles and their properties.

Answer 2

1. Protons - positive charge (+1); Mass (amu) =1
2. Neutrons - neutral charge; Mass (amu) =1
3. Electrons - negative charge (-1); Mass (amu) =0.00055

Question 3

How is the periodic table organized?

Answer 3

By order of increasing atomic number

Question 4

What is a family or group of elements?

Answer 4

Each column in the periodic table is a family or group of elements. Elements within a group usually share chemical properties.

Question 5

Locate each group on the periodic table and list the charge of ions it tends to form.

a. Group 1A
b. Group 2A
c. Group 3A
d. Group 6A
e. Group 7A

Answer 5

a. Group 1A: +1
b. Group 2A: +2
c. Group 3A: +3
d. Group 6A: -2
e. Group 7A: -1

Question 6

Which of the statements about electrons are not true?

a. Electrons repel each other
b. Electrons are attracted to protons
c. Some electrons have a charge of 1- and some have no charge
d. Electrons are much lighter than neutrons

Answer 6

c

Question 7

Which statments about protons are true?

a. Protons have twice the mass of neutrons
b. Protons have the same magnitude of charge as electrons by are opposite sign
c. Most atoms have more protons than electrons
d. Protons have a charge of 1+

Answer 7

b, d

Question 8

Find the atomic number (Z) for each element

a. Fr
b. Kr
c. Pa
d. Ge
e. Al

Answer 8

a. Fr - 87
b. Kr - 36
c. Pa - 91
d. Ge - 32
e. Al - 13

Question 9

How many protons are in the nucleus of an atom of each element?

a. Ar
b. Sn
c. Xe
d. O
e. Tl

Answer 9

a. Ar: 18
b. Sn: 50
c. Xe: 54
d. O: 8
e. Tl: 81

Question 10

List the symbol and atomic number corresponding to each element.

a. carbon
b. nitrogen
c. sodium
d. potassium
e. copper

Answer 10

a. carbon: C 6
b. nitrogen: N 7
c. sodium: Na 11
d. potassium: K 19
e. copper: Cu 29

Question 11

List the name and the atomic number corresponding to the symbol for each element.

a. Mn
b. Ag
c. Au
d. Pb
e. S

Answer 11

a. Mn: Manganese 25
b. Ag: Silver 47
c. Au: Gold 79
d. Pb: Lead 82
e. S: Sulfur 16

Question 12

Classify each element as metal, nonmetal or metalloid.

a. Sr
b. Mg
c. F
d. N
e. As

Answer 12

a. Sr: metal
b. Mg: metal
c. F: nonmetal
d. N: nonmetal
e. As: metalloid

Question 13

To what group number does each element belong?

a. oxygen
b. aluminum
c. silicon
d. tin
e. phosphorus

Answer 13

a. oxygen: Group 6A
b. aluminum: Group 3A
c. silicon: Group 4A
d. tin: Group 4A
e. phosphorus: Group 5A

Question 14

What is the atomic number and mass for each isotope?

a. a hydrogen isotope with 2 neutrons
b. a chromium isotope with 28 neutrons
c. a calcium isotope with 22 neutrons
d. a tantalum isotope with 109 neutrons

Answer 14

a. a hydrogen isotope with 2 neutrons: 1, 3
b. a chromium isotope with 28 neutrons: 24, 52
c. a calcium isotope with 22 neutrons: 20, 42
d. a tantalum isotope with 109 neutrons: 73, 182

Question 15

Rubidium has two naturally occurring isotopes: Rb-85 with a mass 84.9118 amu and a natural abundance of 72.17%, and Rb-87 with a mass of 86.9092 amu and a natural abundance of 27.83%. Calculate the atomic mass of rubidium.

Answer 15

Fraction Rb-85 = 72.17% / 100 = .7217; Fraction Rb-87 = 27.83% / 100 = .2783

Atomic mass = (84.9118 amu x .7217) + (86.9092 amu x .2783)

Atomic mass = 85.47 amu

Question 16

An element has two naturally occurring isotopes. Isotope 1 has a mass of 120.9038 amu and a relative abundance of 57.4%, and isotope 2 has a mass of 122.9042 amu and a relative abundance of 42.6%. Find the atomic mass of this element and, referring to the periodic table, identify it.

Answer 16

Fraction isotope 1 = 57.4% / 100 = .574; isotope 2 = 42.6% / 100 = .426

Atomic mass = (120.9038 amu x .574) + (122.9042 amu x .426)

Atomic mass = 121.76&raquo_space;> antimony (Sb)