ST1: Elements Of Life

What is the Afbau principle?

Electrons fill the energy levels with the lowest energy first.

What is the Pauli Exclusion Principle?

Each orbital can hold a maximum of two electrons

What is Hund's rule?

When there are more than one orbital of the same energy, these orbitals are first occupied singly by electrons before pairing

What is the relative mass of a proton?

1 amu

What is the relative mass of a neutron?

1 amu

What is the relative mass of an electron?

0.00055

What is the relative charge of a proton?

+1

What is the relative charge of a neutron?

0

What is the relative charge of an electron?

-1

What is atomic number represented by?

z

What is the atomic number of an element?

The number of protons in the nucleus

Where is all the mass of an atom accounted for?

In the nucleus, as most of the atom is empty space

When an atom gains an electron what does it become?

An anion, a negative ion.

When an atom loses an electron, what does it become?

A cation, a positive ion.

How are atoms arranged on the periodic table?

in order of increasing atomic number

What is the mass number of an atom?

The number of protons + neutrons in the nucleus of the atom

What is mass number represented by?

A

When writing the full symbol for an atom, where must mass and atomic number go?

On the left of the element symbol

What is an isotope?

are atoms with the same number of protons but a different number of neutrons

Why do isotopes of an element react in the same way?

They have the same number of electrons.

What is relative atomic mass (Ar)?

The average mass of one atom of an element, accounting all isotopes and their abundances, relative to Carbon-12

What is relative molecular mass (Mr)?

The average mass of a molecule compared to 1/12 of the mass of a carbon-12

What is relative isotopic mass?

The mass of an atom of an isotope compared to 1/12th of the mass of an atom of carbon-12

What are the 4 different sub shells?

s, p, d, f

How many orbitals & electrons are in the s subshell?

1 orbital, 2 electrons

How many orbitals & electrons are in the p subshell?

3 orbitals, 6 electrons

How many orbitals & electrons are in the d subshell?

5 orbitals, 10 electrons

How many orbitals & electrons are in the f subshell?

7 orbitals, 14 electrons

In what directions do all electrons spin?

clockwise or anticlockwise

What spin must pairs of electrons have in an orbital?

opposite

What is an atomic orbital?

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

How many electrons are held in the first energy level?

2

How many electrons are held in the second energy level?

8

How many electrons are held in the third energy level?

18

How many electrons are held in the fourth energy level?

32

What sub levels are present in the first energy level?

1s

What sub levels are present in the second energy level?

2s 2p

What sub levels are present in the third energy level?

3s 3p 3d

What sub levels are present in the fourth energy level?

4s 4p 4d 4f

What is the shape of an s orbital?

spherical

What is the shape of a p orbital?

dumbbell

In the 3p sub level, what are the size and position of the orbitals?

They are the same size but are at 90° to each other

What was the first atomic theory?

Greek atomic model, suggested all matter was composed of tiny indestructible and invisible particles called atoms (greek word atomos)

What did the greeks say determined the properties of an atom?

shapes

What was the ancient greek atomic model based off of?

reason, not experiments

What was the first atomic model?

Daltons hard sphere model (1803) . Viewed atoms as invisible solid balls

What was the second atomic model?

J.J. Thomson's Plum Pudding Model (1899), ball of positive charge with electrons dotted within

What lead to the discovery of the electron?

Experiments with electrolysis showed atoms could form positive or negative ions. Thompson used this discovery to conduct experiments passing very high voltages through gases at low pressure, which produced cathode rays, which he later showed to be a beam of negative electrons

What was the third atomic model?

Rutherford nuclear model, protons concentrated at the nucleus with electrons orbiting.

How was the idea of a tiny nucleus discovered?

Alpha scattering experiment. Showed most alpha particles passed through gold foil, but some bounced back, showing that most of the mass was concentrated in the center

Who discovered atomic number?

Moseley (1913), bombarded elements with high speed electrons and found that x rays were produced. The frequency of these x rays was characteristic of the element and depended on its atomic number, which led him to realise atomic number was what determined which element an atom is in

Who discovered energy levels?

Bohr (1913), he said that atoms would be unstable if electrons orbited how rutherford said they did

Who discovered the neutron and how?

James Chadwick (1932), bombarded a thin sheet of beryllium with alpha particles and showed that uncharged particles were released

After the big bang, what were virtually all atoms made?

Hydrogen

How did stars form after the big bang?

Gradually groups of atoms came together under the force of gravity. They pulled closer and closer, getting hotter and hotter. Eventually the matter became so hot, it began to glow.

What is nuclear fusion?

When two lighter nuclei join together to give a new, heavier nucleus

How does nuclear fusion occur in a star?

Due to high temperatures, electrons are lost, giving positive nuclei that repel each other. But at high temperatures and pressure in the star, the nuclei have enough kinetic energy and are close enough to overcome the repulsion and fuse together.

What keeps the star shining after nuclear fusion?

High amounts of energy are released in the process

What is silicon burning?

A fusion process that occurs in stars just before they collapse.

What happens during silicon burning?

Each silicon nucleus initially fuses with a helium nucleus

What type of radiation is often released by fusion reactions?

Gamma

Does nuclear fusion release or require energy, what is this called?

Releases high amounts, exothermic

When a star burns hydrogen to helium in the core, what happens and why?

Very high amounts of energy are released, causing an outward pressure, opposing the force of gravity, stopping the star from collapsing into itself

After the hydrogen in the core of a star runs out, what happens?

Due to gravity, the core collapses into itself, leaving a shell of hydrogen and helium behind.

What is the unit for concentration?

moldm^-3 or gdm^-3

What is the equation for concentration

concentration = moles/volume

What unit must volume be in when doing concentration calculations?

dm^3

How do you convert cm3 to dm3

divide by 1000

What is a molecule?

Two or more covalently bonded atoms. Often drawn with a single line between each atom (structural formula)

How can we predict the shape of a simple molecule?

The idea of repulsions, sets of electrons around the central atom repel, so get as far apart as possible

What must we do to predict the shape of a simple molecule?

Draw a dot and cross diagram and count how many sets of electrons there are around the central atom

What do all electron pairs do to one another? What is the difference between lone and bonding pairs?

They repel each other, lone pairs repel more than bonding pairs

What is the shape of a molecule with 4 sets of bond pair electrons and why?

Tetrahedral because they all repel each other

What is the shape of a molecule with 3 bond pairs and 1 lone pair and why?

Pyramidal, lone pairs repel slightly more as they're closer to the central atom

What is the bond angle of a pyramidal molecule?

107

What is the shape of a molecule with 2 bond pairs and 2 lone pairs?

non linear

What is the bond angle of a non linear molecule?

104.5

What is the bond angle of a tetrahedral?

109.5

What does a wedge bond show when drawing 3D molecules?

The atom is coming toward us

What does a dashed bond show when drawing 3D molecules?

The atom is going away from us

Are bond pairs or lone pairs closer to the central atom and why?

lone pairs, they are only attracted to one nucleus, the one that is the central atoms

Which type of pair of electrons has the greatest repulsion from the others?

Lone pairs because they are closer to the central atom

What shape does a molecule with 3 sets of electrons make?

trigonal planar shape

What is the bond angle for a trigonal planar shape?

120

When double bonds are present, what happens to the repulsion of lone pairs?

Their repulsion is cancelled out due to the extra electron density in the double bonds

What shape do molecules with 2 sets of electrons make?

linear

What is the bond angle for a linear molecule?

180

Where in the periodic table is it possible for a molecule to have more than 4 electron pairs?

period 3 or below, as shell 3 can accommodate more than 8 electrons due to the d orbitals

If there are more than 4 pairs of electrons around the central atom, what does this mean?

The atom has. ore than 8 electrons in its outer shell. It has used d orbitals to expand the octet

What shape is made when there are 5 electron bonding pairs around the central atom?

Trigonal Bipyramidal

What are the bond angles for a trigonal bipyramidal molecule?

90 and 120

What shape do molecules with 6 sets of electron bond pairs make?

octahedral

What is the bond angle of an octahedral molecule?

90

What is a multiple bond?

two or more covalent bonds between two atoms.

In a molecule with two double bonds (two sets of electrons) , what shape is made?

linear

What is the first ionisation enthalpy?

The energy needed to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions

What are the three main things that affect first ionisation enthalpy?

Atomic radii, Electron Shielding and Nuclear charge

How does atomic radius affect ionisation energy?

The greater the radius, the lower the first ionisation energy, as there is less attraction between the nucleus and outermost electron

How does nuclear charge affect ionisation energy?

The greater the nuclear charge, the greater the attractive force on the outer electrons, so greater ionisation energy

How does electron shielding affect ionisation energy?

Inner shell electrons shield nuclear charge from outer electrons, so first ionisation energy is lower.