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CHEMISTRY LC HL > Definitions > Flashcards

Definitions Flashcards

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1
Q

State Dalton’s Atomic Theory.

A
  1. All matter is made up of very small particles called atoms.
  2. All atoms are indivisible, they cannot be broken down into simpler particles.
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2
Q

What are cathode rays?

A

Streams of negatively charged particles called electrons. They travel in straight lines from the cathode to the anode, are deflected by electric and magnetic fields and have sufficient energy to move a small object such as a paddle wheel.

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3
Q

What is an energy level?

A

The fixed energy value that an electron in an atom may have.

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4
Q

What is the ground state of an atom?

A

The ground state of an electron is one in which the electrons occupy the lowest available energy levels.

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5
Q

What is the excited state of an atom?

A

The excited state of an atom is one in which the electrons occupy higher energy levels than those available in the ground state.

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6
Q

Define an atomic orbital.

A

A region in space within which there is a high probability of finding an electron.

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7
Q

State Heisenberg’s Uncertainty Principle.

A

Heisenberg’s Uncertainty Principle states that it is impossible to measure at the same time both the velocity and the position of an electron.

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8
Q

What is a sublevel?

A

A sublevel is a subdivision of a main energy level and consists of one or more orbitals of the same energy.

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9
Q

What are Dobereiner’s Triads?

A

A triad is a group of three elements with similar chemical properties in which the atomic weight of the middle element is approximately equal to the average of the other two.

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10
Q

What are Newland’s Octaves?

A

Newland’s Octaves are arrangements of elements in which the first and the eighth element, counting from a particular element, have similar properties.

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11
Q

State differences between Mendeleev’s Period Table and the Modern Periodic Table.

A
  1. Mendeleev arranged elements in order of increasing atomic weight, in the Modern Period Table elements are arranged in order of increasing atomic number.
  2. Mendeleev had only 60 elements, the Modern table has over 100.
  3. Mendeleev left gaps for undiscovered elements.
  4. Transitions elements are put in a separate block in the modern periodic table.
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12
Q

Define the mass number of an element.

A

The mass number of an element is the sum of the number of protons and neutrons in the nucleus of an atom of that element.

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13
Q

What are isotopes?

A

Isotopes are atoms of the same element which have different mass numbers due to the different number of neutrons in the nucleus.

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14
Q

Define relative atomic mass.

A

The average of the mass numbers of the isotopes of the element,
as they occur naturally,
taking their isotopes into account and
expressed on a scale in which the atoms of the carbon-12 isotope have a mass of exactly 12 units.

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15
Q

Explain the principle of mass spectrometry.

A

The principle of mass spectrometry is that charged particles moving in a magnetic field are deflected to different extents according to their masses and are thus separated according to these masses.

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16
Q

Define the Aufbau Principle.

A

When building up the electron configuration of an atom in its ground state, the electrons occupy the lowest available energy levels.

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17
Q

What is Hund’s Rule of Maximum Multiplicity?

A

When two or more orbitals of equal energy are available, the electrons occupy them singly before filling them in pairs.

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18
Q

What is the Pauli Exclusion Principle?

A

The Pauli Exclusion Principle states that no more than two electrons may occupy an orbital and they must have opposite spin.

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19
Q

What is a compound?

A

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

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20
Q

State the Octet Rule.

A

When bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost energy level.

21
Q

What is an ion?

A

An ion is a charged atom or group of atoms.

22
Q

What is an ionic bond?

A

An ionic bond is the force of attraction between oppositely charged ions in a compound. Ionic bonds are always formed by the complete transfer from one atom to another.

23
Q

Distinguish between a sigma bond and a pi covalent bond.

A

A sigma bond is formed by the head-on overlap of two orbitals while a pi bond is formed by the sideways overlap of p orbitals.

24
Q

Define electronegativity.

A

Electronegativity is the relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond.

25
Q

What is a polar covalent bond?

A

A polar covalent bond is a bond in which there is unequal sharing of the pair of electrons. This causes one end of the bond to be slightly positive and the other end to be slightly negative.

26
Q

To predict which compounds are ionic or covalent.

A 
An electronegativity value
>1.7 indicates ionic bonding 
≤1.7 indicates covalent:
       0.4<1.7 indicates polar covalent
       ≤0.4 is pure covalent
27
Q

Define intramolecular bonding.

A

Intramolecular bonding is bonding that takes place within a molecule, e.g. covalent bonding

28
Q

What are intermolecular forces?

A

Intermolecular forces are the forces of attraction that exist between molecules, e.g. VDW forces, dipole-dipole forces and hydrogen bonding.

29
Q

What are Van der Waals forces?

A

Van der Waals forces are weak attractive forces between molecules resulting from the formation of temporary dipoles. They are the only forces of attraction between non-polar molecules.

30
Q

What are dipole-dipole forces?

A

Dipole-dipole forces are forces of attraction between the negative pole of one polar molecule and the positive pole of another polar molecule, e.g. hydrogen chloride.

31
Q

What are hydrogen bonds?

A

Hydrogen bonds are particular types of dipole-dipole attractions between molecules in which hydrogen bonds to highly electronegative elements, N, O or F. The hydrogen atom carries a partial positive charge. The hydrogen bond acts as a bridge between two electronegative atoms in separate molecules, e.g H2O.

32
Q

Define the Law of Conservation of Mass.

A

The Law of Conservation of Mass states that the total mass of the products of a chemical reaction is the same as the total mass of the reactants.

33
Q

Define the Law of Conservation of Matter.

A

The Law of Conservation of Matter states that in any chemical reaction, matter is neither created nor destroyed but merely changes from one form into another.

34
Q

Define the atomic radius (covalent radius) of an atom.

A

The atomic radius of an atom is defined as half the distance between the nuclei of two atoms of the same element that are joined together by a single covalent bond.

35
Q

Define first ionisation energy.

A

The first ionisation energy of an atom is the minimum energy required to completely remove the most loosely bound electron from a neutral gaseous atom in its ground state.

36
Q

Define radioactivity.

A

Radioactivity is the spontaneous breaking up of unstable nuclei with the emission of one or more types of radiation.

37
Q

What is a nuclear reaction?

A

A nuclear reaction is a process that alters the composition, structure or energy of an atomic nucleus.

38
Q

What is the half-life of an element?

A

The half-life of an element is the time taken from half of the nuclei in any given sample to decay.

39
Q

What is a radioisotope?

A

A radioisotope is a radioactive isotope.

40
Q

What is radiocarbon dating?

A

Radiocarbon dating is a technique used to determine the age of an object containing carbon. It is based on the ratio of carbon-14 to carbon-12 in the object.

41
Q

Define a mole.

A

One mole of a substance is the amount of that substance that contains 6x10^23 particles of that substance.

42
Q

What is a gas?

A

A gas is a substance that has no well-defined boundaries but diffuses rapidly to fill any container in which it is placed.

43
Q

State Boyle’s Law.

A

Boyle’s Law states that, at constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure.
pV=k

44
Q

State Charles’ Law.

A

Charles’ Law states that, at constant pressure, the volume of a fixed mass of gas is directly proportional to its temperature measured on the Kelvin scale.

45
Q

State Gay-Lussac’s Law of Combining Volumes.

A

In a reaction between gases, the volumes of the reacting gases and the volumes of any gaseous products are in the ratio of small whole numbers provided the volumes are measured at the same temperature and pressure.

46
Q

State Avogadro’s Law.

A

Avogadro’s Law states that equal volumes of gases contain equal numbers of molecules under the same conditions of temperature and pressure.

47
Q

What is an ideal gas?

A

An ideal gas is one that perfectly obeys all the assumptions of the kinetic theory of gases under all conditions of temperature and pressure.

48
Q

How do real gases differ from ideal gases?

A

Real gases differ from ideal gases because

forces of attraction

CHEMISTRY LC HL (1 decks)

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