Atomic Structure Intro

Question 1

Describe a pure substance

Answer 1

• has constant properties and composition aka. made of one type of atom
• all matter can be separated into pure substances
• they can be elements or compounds and are changed via chemical reactions

Question 2

What is the law of definite proportions?

Answer 2

Law that a chemical compound maintains at a fixed ration regardless of source or amount

Question 3

What is the law of multiple proportions?

Answer 3

The law that when 2 elements combine, the ratio of the 1 element that combines with the fixed weight of the element are whole numbers.

Question 4

Isotope

Answer 4

Atoms of same element with different mass no.

Question 5

Atomic number

Answer 5

• Number of protons (= number of electrons)

- Bottom number for element on periodic table

Question 6

Mass number

Answer 6

• Number of protons and neutrons combined

- Top number for element on periodic table

Question 7

What is a unit of mass

Answer 7

It is 1/12th of carbon 12 (also called Dalton/D1)

Question 8

What is relative atomic mass

Answer 8

It is the ratio of the mass of one atom of an element against the mass of 1/12th of an atom of carbon 12

Question 9

What is relative molecular mass?

Answer 9

The ratio of the average mass of a molecule to the mass of one 1/12th of an atom of carbon 12

Question 10

What is Avogrado’s constant?

Answer 10

The number of atoms in 12g of carbon 12

6.022045 10^23/mol

Question 11

What is molar mass (and equation)

Answer 11

Molar mass = grams/mole

- sum of the total mass in grams of all the atoms that make up a mole of particular molecule

Question 12

What is electronegativity? (Describe)

Answer 12

• Tendency of an atom to attract a pair of shared electrons
• happens for covalent bonds
• affected by atomic number and the distance of the valence bonds from the nucleus

Question 13

Homonuclear

Answer 13

Multiple molecules of the same element

Question 14

Heteronuclear

Answer 14

Multiple of molecules of different elements

Question 15

Disassociation energy

Answer 15

Energy required to fracture a bond between atoms

Question 16

What are the 3 different electronegativity scales

Answer 16

Pauling scale = mean difference between average disassociation energies homo and heteronuclear compounds of an element

Alfred- Rochow = value of electrostatic force exerted by nuclear charge of valence electrons

Mullikan - average ionisation energy and electron affinity of element

Question 17

Describe an atom

Answer 17

• nucleus positively charged and consists of protons (+) and neutrons (0)
• shells negatively charged and consist of electrons (-)
• shells 100,000 times larger than nucleus
• nucleus contains 99.9% of mass

Question 18

Describe how periodic table can be used to observe ionisation

Answer 18

• Increases across periods as energy also increases to remove electron and atomic radius decreases = greater attraction between electrons and nuclei
• Decreases as atomic number increases/down a group
• noble gasses don’t want to react = least likely to ionise

Question 19

Describe relationship between periodic table and electron affinity

Answer 19

• increases across periods
• sometimes decreases down a group
• low for noble elements

Question 20

Describe electron shells and sub shells

Answer 20

• shells are discrete (not in between energy transitions)
• shells contain max 2n^2 electrons
• shells divide into sub shells S (2 electrons), P (6), D (10), F (14)
• mains shell 1 = 1s (2 electrons)
• mains shells 2 = 1s and 1p (8 electrons)
• mains shell 3 = 1p and 1 d (18 electrons)
• s shells spherical
• p shells figure of 8

Question 21

Describe electron orbitals

Answer 21

• function probabilities (95%) of electron being present

- no of sub shells reflect spatial orientation

Question 22

Describe energy levels of electrons

Answer 22

divided into 4 quantum numbers, electrons will differ in at least 1 of them:

• principle quantum number, n (size of orbitals)
• angular quantum number, l (shape of orbitals)
• magnetic quantum number, m (orientation of orbitals)
• spin quantum number, s ( all electrons need different spins.. spins clockwise on axis = spin up, counterclockwise = spin down) if spins unpaired = reactivity

Question 23

How to work the relative atomic mass

Answer 23

Add together the mass number of each element

Question 24

How to work out molecular mass

Answer 24

1. Determine molecular formula
2. Find atomic mass of each element
3. Multiple atomic mass by number of that element in the molecule
4. Add values together

Question 25

How to work out the number of moles

Answer 25

Number of moles = mass x relative molecular mass

Question 26

Molar concentration/molarity

Answer 26

Number of moles of a solute that can dissolve in 1 litre of solution

Question 27

Molarity equation

Answer 27

Amount of solute (in moles) / volume of solution (L)