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Chemistry exam questions > Definitions > Flashcards

Definitions Flashcards

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1
Q

Element

A

A substance that cannot be broken down into simpler substances by chemical means or produced by combining simpler substances.

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2
Q

Metal

A

Any element that loses electrons to form a positive ion (cation).

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3
Q

Atomic number

A

The number of protons present in the nucleus of an atom.

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4
Q

Mass number

A

The mass number is the number of protons plus neutrons present in the nucleus of an atom.

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5
Q

Isotopes

A

Isotopes are atoms of the same element that have the same atomic number but different mass numbers due to the different numbers of neutrons present in the nucleus.

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6
Q

Relative atomic mass number

A

The average mass of an atom of an element compared to 1/12 the mass of the carbon-12 isotope, taking relative abundances of the naturally occurring isotopes into account.

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7
Q

Relative molecular mass number

A

The average mass of a molecule of a compound compared to 1/12 the mass of the carbon-12 isotope, taking relative abundances of the naturally occurring isotopes into account.

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8
Q

Compound

A

A compound is a substance that is made up of two or more elements combined together chemically.

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9
Q

The octet rule

A

This rule states that when atoms bond, most atoms tend to want an electron arrangement of eight electrons in their outermost shell (energy level).

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10
Q

Valency

A

The valency of an atom tells us the number of chemical bonds an atom can form.

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11
Q

Radioactivity

A

Is the spontaneous disintegration of the nucleus with the emission of α, β or y radiation.

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12
Q

Nuclear reaction

A

A nuclear reaction involves a change in the nucleus of an atom and a new element is usually formed as a result.

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13
Q

Chemical reaction

A

A chemical reaction involves electrons being shared or transferred from one atom to another - the nucleus of the atom remains the same.

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14
Q

Half-life

A

This is the time taken for half the nucLEI in a given sample size to decay.

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15
Q

The principle (mass spectrometer)

A

The principle involved is that different ions are separated according to their masses when moving in a magnetic field.

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16
Q

Absorption spectrum

A

An absorption spectrum is a series of dark lines against a coloured background.

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17
Q

Emission spectrum

A

An emission spectrum is a series of coloured lines against a dark background.

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18
Q

Heisenberg’s uncertainty principle

A

This states that it is impossible to know both the position and the speed of an electron at the same time as electrons move in a wave motion.

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19
Q

Atomic orbital

A

An atomic orbital is a region in space around the nucleus of an atom in which there is a high probability of finding an electron.

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20
Q

Energy level

A

Is the discrete amount of energy an electron has when it is in an atom.

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21
Q

Energy sublevel

A

A group of atomic orbitals within an atom, all of which have the same energy.

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22
Q

Aufbau principle

A

Electrons occupy the lowest available energy level.

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23
Q

Hunds rule of maximum multiplicity

A

When two or more orbitals of equal energy are available (i.e 2px 2py 2pz), electron fill them singly before filling them in pairs.

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24
Q

Pauli exclusion principle

A

No more than two electrons can occupy an orbital and this they can only do if they have opposite spin.

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25
Q

A mole

A

A mole of a substance is that amount of it which contains the Avogadro’s constant number of particles.

26
Q

Avogadro’s constant

A

Is the number of carbon atoms in exactly 12 grams of the C-12 isotope. This equals 6 x 10(23) particles.

27
Q

Avogadro’s law

A

Equal volumes of all gases measured at the same temperature and pressure contain equal numbers of molecules.

28
Q

Molar mass

A

The mass of one mole of a substance is its relative atomic mass (Ar) expressed in grams.

29
Q

Molar volume

A

At s.t.p the volume of 1 mole of any gas is 22.4 litres (22,400 cm3).

30
Q

Atomic radius (covalent radius)

A

The atomic radius is obtained by getting half the distance between the centers of singly bonded atoms of the same element.

31
Q

Alkali

A

An alkali is a base that is soluble in water.

32
Q

Energy sublevel

A

A group of atomic orbitals within an atom, all of which have the same energy.

33
Q

Transition element

A

An element that forms at least one ion with a partially filled d-sublevel.

34
Q

D-block element

A

An element whose highest energy electron enters a d-orbital.

35
Q

Acids - Arhenius’ theory

A

An acid produces H⁺ ions in water.

36
Q

Monobasic acid

A

A monobasic acid produces one H⁺ ion in solution eg. HCl

37
Q

Dibasic acid

A

A dibasic acid produces two H⁺ ions in solution e.g H₂SO₄.

38
Q

Tribasic acid

A

A tribasic acid produces three H⁺ ions in solution e.g H₃PO₄.

39
Q

Bases - Arrhenius’ theory

A

A base produces OH- ions in water.

40
Q

Acid - Bronsted-Lowry theory

A

An acid is a proton (H⁺) donor.

41
Q

Base - Bronsted-Lowry theory

A

A base is a proton (H⁺) acceptor.

42
Q

Amphoteric

A

A substance that can act as both an acid and a base.

43
Q

Conjugate pairs

A

Two substances that differ by one proton.

44
Q

Salts

A

A salt is formed when the H⁺ of the acid is replaced by a metal or NH₄⁺.

45
Q

Strong acid

A

A strong acid is an acid that fully dissociates in solution and is a good proton donor.

46
Q

Weak acid

A

A weak acid is a poor proton donor and only slightly dissociates in solution.

47
Q

Conjugate acid

A

A base plus a H⁺ ion.

48
Q

Conjugate base

A

An acid minus a H⁺ ion.

49
Q

Ionic bond

A

An ionic bond is formed due to the electrostatic attraction between oppositely charged ions caused by the complete transfer of electrons from one atom to another.

50
Q

Electronegativity

A

The relative power of attraction of an atom of an element for the shared pair of electrons in a covalent bond.

51
Q

Oxidation

A

Oxidation of an element occurs when the element loses electrons.

52
Q

Reduction

A

Reduction of an element occurs when the element gains electrons.

53
Q

Oxidation number

A

The oxidation number of an element is the charge an element has or appears to have when it is in compound when certain rules are applied.

54
Q

Oxidation in terms of oxidation numbers.

A

Oxidation is an increase in oxidation number.

55
Q

Reduction in terms of oxidation numbers.

A

Reduction is a decrease in oxidation number.

56
Q

Boyles law

A

When a fixed mass of gas is kept at constant temperature, its volume multiplied by its pressure is constant.

57
Q

Charles law

A

This states that the volume of a fixed mass of gas, kept at constant pressure, is directly proportional to the absolute temperature (kelvin).

58
Q

Gay-Lussac’s Law of combining volumes

A

This states that gases always react with each other in simple whole number ratios when the volumes are measured at the same temperature and pressure.

59
Q

Avogadro’s Law

A

This states that equal volumes of gases measured under the same conditions of temperature and pressure contain equal numbers of molecules.

60
Q

An ideal gas

A

An ideal gas is defined as a gas that obeys all gas laws at all temperatures and pressures.

Chemistry exam questions (29 decks)

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