Chapter 2

Question 1

Law of conservation of mass

Answer 1

1. Mass is conserved during physical and chemical transformations
   2 the number of atoms of each element is conserved in a chemical reaction.

Question 2

Electrons

Answer 2

Small, negatively-charged particles
Very small mass
Found in a cloud surrounding the nucleus

Question 3

Neutrons

Answer 3

Neutral particles

Found in the nucleus

Question 4

Protons

Answer 4

Positively charged particles

Found in the nucleus

Question 5

What 4 experiments did scientists perform in the early 1900s?

Answer 5

1. Gas discharge experiment
2. Cathode ray tube experiment
3. Oil drop experiment
4. Gold foil experiment

Question 6

Gas discharge experiment

Answer 6

Finding: atoms contain smaller parts that possess positive and negative charges.

Question 7

Cathode Ray Tube

Answer 7

Determined ratio of the electrons charge to its mass.

Ratio (Charge/Mass) = -1.76 X 10^11 C/kg

Question 8

Oil drop experiment

Answer 8

Millikan determined the charge and mass of an electron.

Charge: -1.6 X 10^-19 C
Mass: 9.1 X 10^-19 kg

Question 9

Rutherford’s Gold Foil Experiment

Answer 9

Discovered how charge and mass are distributed in atoms.
• each atom must have a small core called a nucleus
• the nucleus must contain all the positive charge
• most of the atoms mass must be concentrated in the nucleus
• the size of the nucleus of an atom compared to the atom itself is like the size of a pea compared to a baseball stadium, and that pea would have a mass of 250 million tons.

Question 10

Isotopes

Answer 10

Atoms with the same number of protons, but different number of neutrons.

Isotopes are specified by their mass numbers.

• a mass number is the sum of the number of protons and neutrons in an isotope.

Question 11

Mass Spectoscopy

Answer 11

Mass spectroscopy (MS) can be used to study isotopes
• separates charged particles according to their masses.
• produces a graph (mass spectrum) of ions abundances

Question 12

Alpha Decay

Answer 12

Emission of an energetic helium

Question 13

Beta Decay

Answer 13

Emission of a high kinetic energy electron

Question 14

Positron emission

Answer 14

Emission of a particle with the mass of an electron but with a positive charge

Question 15

Counting atoms

Answer 15

To count to number of atoms, we refer to the number of atoms with the unit the mole (mol)

1 mol of atoms= 6.022142 X 10^23 atoms
Avogadro’s Number = 6.022 X 10^23

Question 16

Molar Mass

Answer 16

The molar mass (MM) of any substance is the mass of one mile of that substance.

MM units:

g/mol
Amu

The MM for each element can be found on the periodic table

The MM (as listed on the periodic table) of any naturally occurring element is the weighted sum of the contributions from its isotopes.

Question 17

Ions

Answer 17

Atoms are neutral if they have the same number of protons and electrons.

Atoms may gain or lose electrons to form charged particles.

Electrically charged atoms or molecules are called ions.

• cations are positively (+) charged particles
• anions are negatively (-) charged particles

Question 18

Cation formation

Answer 18

Cations are positively (+) charged particles

Cations are formed by the loss of an electron.

Question 19

Anion Formation

Answer 19

A ions are negatively (-) charged particles

A ions are formed by the gain of an electron

Question 20

Neutral ionic compound

Answer 20

Is a solid that contains cations and anions in balanced whole-number ratios

• compounds must by neutral to be considered stable
• the amount of positive charge must balance the amount of negative charge.

Question 21

Atomic Theory

Answer 21

Developed by John Dalton

1. All matter is composed of tiny particles called atoms.
2. All atoms of a given element have identical chemical properties that are characteristic of that element.
3. Atoms form chemical compounds by combining in whole number ratios
4. Atoms can change how that are combined, but they are neither created nor destroyed in chemical reactions