Matter, Atomic Structure, Moles

element

the simplest form of matter than cannot be broken down any further by physical nor chemical means

Elements are identified based on their number of ______

the number of protons each of their atoms have

Compound

substance formed when two or more elements are chemically bonded together in a fixed ratio

mixture

two or more, elements, compounds or both combined physically but not chemically bonded

True or false: compounds & elements are pure substances?

true

common techniques of physically separation include

• filtration

• recrystallisation

• evaporation

• distillation

• paper chromatography

homogenous mixtures

• uniform composition

• particles are evenly distributed — composition is consistent throughout

heterogenous mixtures

• non-uniform composition

• particles are not evenly distributed

when to use filtration

• separate insolube solids from liquids

when to use recrystallisation

when purifying a solid substance

how does recrystallisation work

relies on difference in solubility

purpose of evaporation

removes a liquid from a solution by heating it (leaving a dissolved solid)

examples of “stubborn” heterogenous mixtures

• smoke

• milk

• tea + milk

• pepsi

purpose of distillation

separates two or more liquids with different boiling points

ex. separating ethanol from water

how does distillation work

the liquid with the lower boiling point evaporates first, is condensed (cooled) then collected

when to use fractional distillation

when aiming to physically separate substances of similar boiling points

purpose of paper chromatography

separates a mixture based on differences in solubility & polarity

how does paper chromatography work

substances of a particular polarity will dissolve better in a substance of the same polarity (non-polar solute in non-polar solvent, and vice-versa)

• the solutes with higher affinity to water will travel further up the page

• the solute with higher affinity to paper will travel less distrance

• subtances with smaller molecules move faster across the paper

in paper chromatography the paper is referred to as…

stationary phase

in paper chromatography the water is referred to as…

the mobile phase

nucleons

the particles found within the nucleus of an atom (protons and neutrons)

nucleus

dense positively charged core that contains nucleons

purpose of neutrons

offset the repulsion between protons —stabilising the nucleus

isotopes

atoms of the same elements that contain a different number of neutrons

what do the letters A & Z represent

Z = atomic number (number of protons)

A = mass number (# of protons + # of neutrons)

Where are electrons found

Very likely to be in orbitals (likely within the electron cloud)

What is chemical behaviour based on?

number of electrons at atom has

relative atomic mass (Aᵣ)

the weighted average of the masses of an elements isotopes with respect to their to natural abundances

formula for relative atomic mass (Aᵣ)

Aᵣ = ((mass of isotope x abundance) + (mass of other isotope x abundance))/100

how to calculate abundance of isotopes

let the abundance of one isotope be x and the other be 100-x (or 1-x)

• then use algebra to find values (solve for x)

what are possible differences between isotopes (and other isotopes)

• (natural) abundance

• mass

• physical properties (boiling point, melting point, solubility, mass)

what does the formula E = h x f represent

the energy of a photon

what does this symbol represent

wavelength

what does this symbol represent

speed of light

how/why do line emission spectra appear

they arise from the transitioning of electrons between specific energy levels

emission spectrum

bright lines corresponding to specific wavelengths of light emitted by an atom

absorption spectrum

dark lines against a continuous background

• the dark lines correspond to wavelengths of light absorbed by at atom when an electron excites moving to a higher energy level

emission spectrum

bright coloured lines against a dark background

• the colours correspond to a particular wavelength of light

when/how are line emission spectrum produced

when a pure gaseous element is subjected to high voltage under reduced pressure —it emits light

• the light is then passed thru a prism which produces the line emission spectrum

why are line emission spectrums different per element

because the electrons of each element’s atoms can only occupy certain 9specific/discrete) energy levels

what form of energy do electrons release when jumping descending from higher energy level to lower

photon

what is the strcuture of hydrogen line emission spectrum

the lines converge at higher energy levels

describe the wavelength of light of an electron transitioning from a higher energy level to n = 1, n = 2 and n = 3

higher energy level → n = 1 = uv region

higher energy level → n = 2 = visible light region

higher energy level → n = 3 = infrared region

what is the formula to calculate the (total) maximum number of electrons in an energy level

2n²

• n is the principal quantum number (number of energy levels there are)

Hund’s rule

electrons will fill orbitals singly (all with the same spin) before pairing

Pauli’s exclusion principle

two electrons (an electron pair) sharing an orbital will have opposite spins

where are noble gases located on the periodic table

group 18 (helium, neon, argon, krypton etc)

describe the position of electrons in ions

• cations lose electrons from the highest energy level (outermost shell)

• anions gain electrons into the highest energy level (outermost shell)

full electron copper (Cu)

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰

full electron configuration of chromium (Cr)

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵

why are copper & chromium exceptions for electron configurations

their half/fully-filled d-sublevels are more stable due to reduced electron repulsion (thus less likely to lose electrons)

N = number of entity (whether that be atoms, molecules, ions etc)

n = amount of substance in moles

Nₐ = avogadro’s constant

how to calculate the molar mass of a compound

add up the atomic mass of each atom within the compound

• (each atom’s atomic mass is multiplied by the number of atoms of it there are present in the compound)

• ex. to find the molar mass of CO₂ = molar mass of Carbon + (molar mass of Oxygen x 2) fetched from the periodic table

calculating relative formula mass (Mᵣ)

1. relative atomic mass of each atom in chemical formula x number of atoms of that element present

2. add the products together

what unit does molar mass use

g mol ⁻¹ (“grams per mol”)