Unit 1 - Matter, Chemical Trends and Bonding

Question 1

What is empirical knowledge?

Answer 1

knowledge that comes from investigation and observation

Question 2

What is theoretical knowledge?

Answer 2

applying knowledge to explain scientific observations

Question 3

What is an atom?

Answer 3

• the smallest unit of an element that can be divided and still be that element
  Example: The smallest particle of carbon is a single atom of carbon. If you divide it is no longer carbon anymore

Question 4

Atomic Theory - Democritus + what did he propose?

Answer 4

theorized that matter is composed of tiny, indivisible particles called atomos

Proposed:
-Atoms are small hard particles.
-Made of a single material that’s formed into different shapes and sizes
- They are always moving
- They form different materials by joining together.

Question 5

Atomic Theory - Dalton + what did he propose?

Answer 5

• Elements are composed of small, indivisible particles called atoms and that each unique element is composed of a single type of atom
• Atoms of one element are different from the atoms of all other elements
• During chemical reactions, atoms are combined, separated, or rearranged into different ratios

Question 6

Atomic Theory - JJ Thompson + what did he propose?

Answer 6

• Performed experiments with cathode ray tubes
• When charged electric plates are placed around the cathode ray, the beam veered away from the
  negatively charged plate
• By measuring the deflection of the rays, he was able to determine that the particle was two thousand times lighter than a hydrogen atom

CONCLUSION:
- a sub-atomic particle exists
- this sub-atomic particle is negatively charged (ELECTRON)

Question 7

What is the Thompson model?

Answer 7

• Plum pudding
• First model to confirm that atoms are made up of smaller subatomic particles
  Knew that atoms were neutral, so a positively-charged particle must also exist

Question 8

Atomic Theory - Rutherford + what did he propose?

Answer 8

• Performed the gold foil experiment (Shot positively charged alpha particles (He2+) through a thin sheet of gold and based on Thomson’s model, most of the particles should have gone straight through)
• While most alpha particles went through the foil, some were deflected at large angles
• Rutherford theorized that the alpha particles were hitting something dense and positively-charged

Question 9

What is the Rutherford model?

Answer 9

The planetary model
- Proposed that the positively charge of an atom was concentrated in the centre of an atom
- Electrons orbits the nucleus like planets

Question 10

Issues of the Rutherford model?

Answer 10

• nucleus composed only of positive charge should break apart due to electrostatic repulsion
• The positively-charged particles could not account for the total mass of the atom

Question 11

Atomic Theory - Bohr + what did he propose?

Answer 11

• observed that the hydrogen atoms emitted
  light of only certain colours when they were
  ”excited”

Question 12

What is the Bohr model?

Answer 12

• Electrons orbit the nucleus of the atom in definite energy levels
• Electrons can “jump” between orbits by absorbing or emitting photons carrying an amount of energy that is equal to the difference in the energy levels of the electrons

Question 13

What is an isotope?

Answer 13

Atoms of an element with the same # of protons but different # of neutrons

Question 14

What is isotopic abundance?

Answer 14

The % of an isotope in a sample of an element

Question 15

What is atomic mass?

Answer 15

The atoms average weight from the isotopes

Question 16

What is a mass spectrometer?

Answer 16

Used to identify isotopes and their relative abundance
1. Vaporization
2. Ionization
3. Acceleration
4. Deflection
5. Detection

Question 17

What is nuclear radiation?

Answer 17

• When some isotopes are unstable and radioactively decay
• Some isotopes decay and emit radiation
  a) Alpha particles (a) -has the same nuclear structure as He-4
  b) Beta particle (β) - Negatively charged electron
  c) Gamma Ray (γ) - Is a form of high-energy electromagnetic radiation

Question 18

What are valence electrons and core electrons?

Answer 18

1. Electrons found in the outermost shell
2. Electrons that aren’t valence electrons (inside)

Question 19

What is atomic radius and its trend?

Answer 19

Defined as the distance from the nucleus to the valence electrons
Trend:
- As you go down it increases
- As you move left to right, it decreases

Question 20

What is a nuclear charge?

Answer 20

The charge of the nucleus
- Core electrons can reduce the positive nuclear charge –> shielding by the outer electrons (to not add anymore electrons –> keep neutral)

Question 21

What is an ionic radius?

Answer 21

When cations form, the number of electron orbits decreases. Each remaining electron feels a stronger attraction to the nucleus

• When anions form, there is more electron-electron repulsion Zeff is ”shared” among more electrons

Question 22

What is electron affinity?

Answer 22

The amount of energy needed to gain an electron

Question 23

What is electronegativity?

Answer 23

The atoms ability to attract electrons

Question 24

What is ionization?

Answer 24

How much energy it takes for an atom to lose an electron

Question 25

What is the structure of ionic compounds?

Answer 25

They form a crystal lattice structure
- The smallest repeating unit is called a formula unit

Question 26

What are the properties of ionic compounds?

Answer 26

• High melting and boiling point
• Solid at room temp –> strong electrostatic forces
• Many are soluble in water
• Conduct electricity well
• Hard but brittle
  ex. When you hit a hammer on it, the structure changes and cause the like charges to repel and break

Question 27

What are the properties of molecular substances?

Answer 27

• Exist as gases, liquids, and solids at room temp
• Low boiling points and melting points
• Poor conductors of electricity
• Do not dissolve in water

Question 28

What is covalent bonding?

Answer 28

When a pair of electrons are shared by 2 atoms + molecular

Question 29

How to tell if something is ionic or molecular?

Answer 29

Calculate the electronegativity difference between 2 elements

Question 30

What are non-polar bonds?

Answer 30

Equal sharing of electrons

Question 31

What are polar bonds?

Answer 31

Unequal sharing of electrons (positive and negative charges)
- Have charged ends

Question 32

What is intramolecular forces?

Answer 32

Within a molecule (ionic and covalent bonds)

Question 33

What are intermolecular forces?

Answer 33

Forces of attraction between molecules which determine the physical properties (stronger intermolecular forces = stronger physical properties) (dipole dipole, london, hydrogen)

Question 34

What is dipole-dipole forces?

Answer 34

Negatively charged ends attract to the positively charged end
- Permanent
- Polar bonds

Question 35

What is london dispersion forces?

Answer 35

When a negative and positively charge create a temporary charge accidentally

Question 36

What is hydrogen bonding?

Answer 36

When hydrogen atoms bonds with N, O, F

Question 37

Why is water dense?

Answer 37

• The solid state of most compounds is more dense than the liquid state, so the solid therefore sinks in the liquid
• Ice, however, is less dense than liquid water so it floats in liquid water
• This is because the hydrogen bonds in water arrange the molecules in a crystalline structure, leaving gaps between molecules

Question 38

What causes surface tension?

Answer 38

• caused by the forces of attraction between molecules at the surface of the liquid

Question 39

What is viscosity?

Answer 39

In general, the stronger the intermolecular forces, the higher the viscosity of the liquid
- describes a liquid’s resistance to flow

Question 40

What is the pattern of solubility?

Answer 40

• Polar substances tend to dissolve well in polar solvents, while non-polar substances tend to dissolve well in non-polar substances (like dissolves like)
• Due to water’s polarity, when ionic or polar substances are added to water, new intermolecular forces are formed between water molecules and the solute