Atomic structure and the periodic table
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What is the structure of an atom?
A nucleus consists of protons and neutrons, which have an overall positive charge and is very tiny compared to the size of the whole atom but take up the most mass. Electrons orbit the nucleus in orbitals (shells) and these take up most of the volume of the atom.
define Mass number and where it is on the element symbol Define atomic number and where it is on the element symbol
Mass number: the sum of protons and Neutrons (top number) Atomic number: number of protons (bottom number)
What is the relative mass of an electron?
1/1840
Define isotope
Atoms of the same element but with a different number of neutrons and same number of protons.
Why do isotopes have similar chemical properties?
Because they have the same electronic structure
Why do Isotopes sometimes have slightly varying physical properties?
Because they have different masses.
Define the Relative isotopic mass
The mass of one atom of an isotope compared to one-twelfth of the mass of one atom of carbon-12
How do you calculate the relative atomic mass?
100
define first ionisation energy
the energy takes to remove 1 mole of electron from one mole of an element to form 1 mole of an ion.
what three factors affect ionisation energy
Nuclear charge: the more protons in an atom, the more positively charged the nucleus is, and the stronger the attraction. electron shell: attraction falls rapidly with distance, so if a shell is closer to the nucleus, it will be more strongly attracted to it. Shielding: The lessening of the pull of the nucleus- the further away the shell is, there’s less shielding, so easier to pull away the electron.
Why do ionisation energies decrease down a group?
• elements further down a group have more energy levels • so electrons are farther away from the nucleus each time • so they’re less attracted to the nucleus • the extra inner shells shield the outer electrons from the attraction of the nucleus.
How many electrons does the 3rd energy level hold?
18
how many electrons do each of the subshells hold?
s- 2 p- 6 d- 10 f- 14
state the order of subshells in an atom
1s 2s 2p 3s 3p 3d 4s 4p 4d 4f
what is the Aufbau principle
the idea that the lowest energy levels are filled first.
define the empirical formula
the simplest whole-number ratio of the atoms present in the element.
Define the molecular formula
The actual number of each type of atom in a compound
How do you determine the % composition of elements in a compound?
workout the Mr, then do Ar of each element/ Mr x 100
How does atomic radius change from: Across a period Down a group
Increase decreases
how does nuclear charge change across a period down a group
Increases Increases
How does Shielding change across a period down a group
stays constant- electrons are being added to the same energy level Increases
why does ionisation energy decrease from group 2-3
Because in group 3, the highest subshell is p, whereas it’s s in group 2. This means that its further away from the nucleus and there is less attraction between the nucleus and electrons, making it easier to remove an electron
Why does ionisation energy decrease from group 5-6
Even though electrons are being added, it’s to the same subshell. This means that the repulsion between electrons makes them easier to remove the electron.
What are the different stages of mass spectometry? Include which component helps it to take place.
• Ionisation- electron beam fires high energy electrons • Acceleration- negatively charged plates attract positive ions • Deflection: electromagnet creates varying EMFs, depending on their mass-to-charge ratio. • Detection: collector plate which induces a current and then amplifies it to produce a spectrum.