module 1 Flashcards

Question

describe the bore model of an atom

Answer 1

According to the Bohr model of the atom: - electrons can only move with fixed amounts of energy, called energy levels - electrons with the same energy level move in the same circular orbit around the nucleus - orbits closer to the nucleus contain lower energy - each energy level has a maximum number of electrons it can contain, given by 2n^2.

Answer 2

atoms of the same element have different numbers of neutrons

Answer 3

Relative atomic mass = (Mass no. of Isotope 1 x % abundance) + (Mass no. of Isotope 2 x % abundance)/100

Answer 4

A flame test seeks to identify the metal present in a substance by the colour displayed when a small sample of the substance is placed in a blue Bunsen flame.

Answer 5

- White light passed through a prism is spread out into different colours - Source of light can be: Metal sample in a Bunsen flame orGas discharge tube with electricity - The emitted light is passed through a vertical slit, then spread out by a prism - This produces coloured, vertical lines on a black strip, called emission spectrum - Each element has a unique emission spectrum - Atoms of the same element produce the same emission spectrum

Answer 6

- According to the Bohr model of the atom, electrons can only move with fixed amounts of energy, called energy levels. - When an atom is given energy (by heat or electricity), its electrons gain energy and jump from a lower to a higher energy level. - After a short time, the electrons fall back down to their original energy level and release energy as light. - The packet of energy corresponds to a wavelength of light (colour). - The same emission spectrum from the same element supports Bohr’s model that electrons can only move between fixed energy levels.

Answer 7

- does not explain why the maximum amount of electrons in each energy level is 2n^2 -Does not explain why elements in Periods 4 to 7 can place electrons in an ‘outer’ energy level before an ‘inner’ energy level is fully filled,

Answer 8

- Arises out of quantum mechanics - Major energy levels, a.k.a shells, contain sub-shells of similar energy levels; these are referred to as s, p, d, f. - Each sub-shell is associated with 3D regions around the nucleus where its electrons are probably found; these regions are known as orbitals - Each orbital can contain up to 2 electrons of opposite spin (Pauli exclusion principle)

Answer 9

- The lowest energy orbitals are always filled with electrons first (Aufbau principle) - Every orbital in a subshell must first be filled with one electron with the same spin before an orbital can be filled with a second electron (Hund’s rule) - At higher subshells, there are exceptions to this because of the Aufbau principle. - The second electron in an orbital must have the opposite spin to the first electron (Pauli exclusion principle simplified).

Answer 10

Some isotopes are unstable, i.e. they will spontaneously break down over time. - Unstable isotopes are called radioisotopes because, when they break down, they send out particles or energy from their centre along radial lines. - What is emitted from the centre is known as radiation.

Answer 11

- isotopes are unstable when they exist outside of the zone of stability The Zone of Stability is defined as: - Atomic number < 83 - neutron : proton ratio that is 1:1 for atomic number 1-20 - neutron : proton ratio that is 1.3:1 for atomic number 21-50 - neutron : proton ratio that is 1.5:1 for atomic number 51-80

Answer 12

- alpha particle - beta particle - gamma ray

Answer 13

- it is like a helium nucleus (emits 2 neutrons and 2 protons0 - It has a charge of +2 - it has low penetration (stopped by a piece of paper - it is emitted when radioisotope lies beyond atomic number 82 and is very heavy

Answer 14

- it emits an electron - change of -1 - moderate radiation (stopped by 0.5mm of lead) - emitted when radioisotope lies above zone of stability and a neutron converts to a proton and electron

Answer 15

- electromagnetic radiation - no charge - high penetration (stopped by 5cm of lead) -emitted with an alpha or beta particle

Answer 16

- Whenever radioisotopes emit alpha or beta particles, the composition of their nuclei change with an alteration in the number of protons. - This MUST mean that the atom has changed from one element to another. - Nuclear equations communicate what happens to nuclei in a nuclear reaction. - An equation must balance the mass number and atomic number

Answer 17

- The rate of decay of a radioisotope is proportional to the amount of radioisotope present. - It is measured by a term called half-life, which is the time taken for half of the radioisotope to decay. - A long half-life means that decay is slow and radiation is emitted for a long period - A short half-life means that decay is rapid and the total amount of radiation is emitted in a burst.

Answer 18

Periodicity refers to the pattern of similar properties recurring at intervals when examining elements in increasing atomic number.

Answer 19

- Elements in the same group have similar electronic configurations, especially for their valence shell. - More energy shells are added going down a group. - Different sub-shells are filled going across a period.

Answer 20

- Core charge = the no. of protons – the no. of electrons in inner shell(s) - Core charge is a measure of how strongly the nucleus pulls on the outer shell electrons, a.k.a. valence shell electrons

Answer 21

- decreases across a period because the core charge increases and pulls each valence electron closer to the nucleus. - increases down a group because the effect of the core charge is reduced by the presence of more inner shell electrons which repel each valence electron.

Answer 22

the amount of energy required to dislodge an electron from an energy shell of a gaseous atom

Answer 23

ionisation increases across a period and decreases down a group. this is because the core charge increases from left to right across a period, but its effectiveness is reduced going down a group.

Answer 24

as you go across a period electronegativity increases, and it decreases down a group

Answer 25

Electronegativity refers to the ability of an atom to attract an electron into its valence shell (measured on Pauling scale between 0 and 4.0)

Answer 26

For a metal, the chemical reactivity increases as ionisation energy decreases because metals lose electrons when they form a chemical bond. For a non-metal, the chemical reactivity increases as electronegativity increases because non-metals gain electrons when they form a chemical bond.

Answer 27

An ionic bond is the electrostatic force of attraction between a positive ion (cation) and a negative ion (anion).

Answer 28

sharing of electrons between two atoms

Answer 29

- similar electronegativity means they share electrons equally (non-polar covalent bond) - difference in electronegativity of 1.0 to 1.7 means they share electrons unequally (non-polar covalent bond - difference >1.7 means one atom takes the electrons (ionic bond)

Answer 30

Valency is a number that measures the combining power of an element. - For an element forming an ionic compound, the valency refers to the number of charges it possesses when it becomes an ion - For an element forming a covalent compound, the valency is the number of covalent bonds it forms

Answer 31

Valence Shell Electron Pair Repulsion is used to determine the shape of small molecules 1.The electrons in the valence shell of an atom, including electrons shared from other atoms, will exist in pairs. 2.These electron pairs will get as far away from each other as possible in three dimensions. - This is limited when there are double bonds or triple bonds

Answer 32

A molecule with non-polar covalent bonds will be a non-polar molecule, i.e. neutral overall with an even distribution of charges. A polar molecule is neutral overall but has an uneven distribution of charges. A polar molecule can also be referred to as a dipole

Answer 33

1. dispersion forces 2. dipole-dipole forces 3. hydrogen bonding

Answer 34

- random movement of electrons can give rise to a temporary dipole - this can induce a temporary dipole in adjacent molecules - electrostatic forces of attraction arise between the negative and positive poles - Dispersion forces are very weak - However, they increase as the size of atoms increase (more electrons that randomly move) or if the molecule is linear (more likely to have a polar end) - Dispersion forces are always present between molecules

Answer 35

- Electrostatic forces of attraction occur between the negative and positive poles of adjacent polar molecules. - These are weak forces (1/100th the strength of covalent bond).

Answer 36

dipole dipole forces are stronger than dispersion forces. dispersion forces are the force of attraction between non-polar molecules whilst dipole dipole forces are between polar molecules

Answer 37

- If H bonds with any of the three most electronegative elements (N, O or F), it forms a very polar covalent bond. - This H atom will be strongly attracted to the lone pair of electrons on N, O or F on an adjacent molecule; this is known as a hydrogen bond. - This force is strong (about 1/10th the strength of a covalent bond) because the H atom has a small radius and can allow a neighbouring molecule’s negative pole to approach closely.

Answer 38

- melting and boiling point - surface tension - solubility

Answer 39

- The stronger the intermolecular forces, the higher the melting point and boiling point. - More energy is required to move particles away from each other when changing state.

Answer 40

- Very strong intermolecular forces will increase surface tension in the liquid state. -Surface tension refers to the tendency of a liquid to minimise its surface area, - This means molecules pull together at the surface of a liquid.

Answer 41

- The type of intermolecular force that is present will determine the solubility of a substance in a solvent: "like dissolves in like" - Ionic compounds are able to dissolve in a solvent made of polar molecules, but not always.