Fundamental Chemistry Flashcards by Issy Hayes

structure of an atom

nucleus - protons +ve mass 1
neutrons 0 mass 1
electrons orbit -ve mass 0
(results in nucleus +ve and heavy)

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describe element composition

top no. = proton/atomic number
bottom no. = proton+neutron/atomic mass
protons and electrons are =

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as you move across the periodic table …

elements gain more protons

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as you move down the periodic table …

there are more concentric circles of electrons

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whats an isotope and what changes

the same element with different no. of neutrons (changes atomic mass but not chemical properties as charge remains the same

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why are atomic masses not usually a whole number

due to many isotopes of the same element

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what is carbon dating

using the isotope 14C which is radioactive to measure how old something is

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whats the half life of 14C and why is that important

5730 yrs and is fixed so at death, organic ,matter has 100% of its 14C, 5730 yrs later it will only have 50% of 14C

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what are anabolic steroids and how are they tracked

elemental isotopes - when testosterone or DHEA is metabolised into androsterone naturally there is specific ratios of 12C and 13C. when synthetically added there is a different ratio however difficult to track due to varying diets

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what stops electrons flying away

attraction between +ve nucleus and -ve electrons

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where are electrons found

orbitals

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whats the octet rule

when electron shells fill sequentially

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why are noble gases inert (don’t react)

they have a full outer shell of electrons (stable octet)

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how to calculate an elements atomic mass with isotopes

isotope no. x %abundance + any other isotope / 100

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ionic bonding

metal x non metal
transferring electrons

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covalent bonding

non mental x non metal
share electrons

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metallic bonding

share a sea of delocalised electrons
metal x metal

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ionic bonding example NaCl

Na atomic no. = 11 (2,8,1)
Cl atomic no. = 17 (2,8,7)
Na needs to donate e- (becomes +ve)
Cl needs to gain e- (becomes -ve)

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properties of ionic bonding

high melting and boiling due to permanent charges forming strong intermolecular forces
soluble as polar
conduct electricity in solution as free movement of charge
brittle as sheets of lattice can slide

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covalent bonding example H2O

H atomic no. - 1
O atomic no. = 8 (2,6)

2xH atoms share each of their electrons (one bond) to fill one O outer shell to 8 by forming 2 bonds

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covalent bonding properties

low melting and boiling as no charge so weaker intermolecular forces
low solubility
don’t conduct electricity and no free movement of electrons

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double covalent bond example CO2

C has 4 electrons in outer shell (requires 4 to be stable)
O has 6 electrons so requires 2
C shares 2 electrons with each O forming 2 double bonds

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triple covalent bonds example hydrogen cyanide

C shares 4
H shares 1
N shares 3

(C-H is one bond sharing 1 electron)
C-N is three bonds sharing remaining 3 electrons)

metallic bonding properties

sea of delocalised electrons means conduction of electricity and malleable

importance of molecular shapes

influences chemical behaviour recognition and response to other molecules

sub levels of energy in electron shells

s = up to 2 e (1pair) p = up to 6 e (3pairs) d = up to 10 e (5pairs) f = up to 14 e (7pairs) (e exist in pairs so each orbital is a pair)

how do the shapes of molecules form

depends on no. of electron pairs in outer shell they exist in a charge cloud which repel each other so want to be as far apart as possible not uniform as if not shared they repel more

shapes of molecules example BeF2 linear

2 pairs around central atom F = 1 pair Be = 2 spare 2xF contribute to sharing e- all e- in outer shell are involved most energetically favourable way to separate is 180 degrees (straight Line F-Be-F)

what causes different molecular shapes to form

lone pairs of electrons which have more repulsion

why does molecular shape matter

results in polarity eg CO2 all e- involved = linear (O-C-O) with charge cancelled out so non polar H2O has 2 spare pairs forming 2 dipoles with O -ve and H +ve and therefore polar

whats electronegativity

ability of an atom to attract electron density towards itself (pulling the -ve causing temporary charge)

whats electronegativity measured in

ability of an atom that is bonded to another to attract electrons to itself (each element given a value between 3.98-0.79)

what happens to electronegativity moving left along periodic table

increases due to outer shell staying same distance from nucleus but nucleus gains more neutrons and protons (more +ve) so the pull from nucleus is stronger

what happens to the electronegativity moving down the periodic table

decreases as outer shell gets further away so the pull is lower and easier to steal e-

whats the electronegativity for non polar covalent bonds

delta E <0.5

whats the electronegativity for polar covalent bonds

>0.5deltaE<2

whats the electronegativity for ionic bonds

deltaE>2

how to calculate electronegativity of a molecule

net difference in value = deltaE

what determines level of polarity

difference in electronegativity between the 2 atoms in the bond egblue = lower electron density red = higher the larger the delta E the more electrons are drawn from one end to the other

why is polarity important

polar molecules are soluble in water steroids are non polar so don't dissolve easily in blood transportation in and out cells

intramolecular vs intermolecular forces

intra within eg covalent inter between molecules (weaker)

how are London dispersion forces formed

constant motion of electrons in the cloud causes temporary charges to form so +ve and -ve attract

dipole dipole attractions

permanent state of polarisation causes. molecules to attract to teach other eg HCl as Cl is -ve and H is positive due to withdrawal of electron density towards Cl

water and hydrogen bonds

O is electronegative and draws electrons from H forming delta -ve O and +H

intermolecular forces with ionic bonding

ionic means transfer of electron = permanent charge attracting atoms together = lattice = high boiling point

importance on ionic bonds in biology

determine shells of proteins ionic solution maintain cell potentials muscle contraction as a result on ion movement

whats a functional group

an arrangement of atoms that's responsible for chemical characteristics found along carbon backbone of organic molecules

hydroxyl group

one form O2 boned to H and organic molecule (carbon) polar bond between O and H and O and R

amine group

contains N and lone pair of electrons class depends on what else is bonded eg primary 1xR secondary 2xR tertiary 3xR (AA primary)

carbonyl group

carbon double bonded to O2 and 2xside chains C +ve and O2 electronegative = polar

acid vs base/alkaline

acid = more H+ ions

importance of ph in biology

requires specific ph to function eg exercise increases H+

Avogardos constant

the mole = 6.02x10^23

whats molecular concentration

number of moles of a substance in a defined volume (1 mole of a molecule is always its molecular weight)

calculation of molarity

Mass = Molecular weight x Moles Molecular weight = Mass/Moles Moles = Mass/Molecular weight