Chem Semester One

why are valence electrons important for stability?

as when the shell is filled, it is stable. incomplete valence shells are highly reactive and participate in various reactions

why are valence electrons shells lost so easily?

they are farther from the nucleus and experience less electrostatic attraction

shielding effect

inner shell electrons reduce the effective nuclear charge felt by outer shell electrons

electrostatic attraction

the force of attraction between oppositely charged particles, while same charges repel

4 stages of mass spectrometry

ionisation, acceleration, deflection, detection

ionisation

knocking electrons off atoms to produce ions

acceleration

charged plate accelerates cations

deflection

the ions are deflected in a magnetic field

detection

a computer analyses which isotopes are present and their abundance

chemical properties of isotopes

similar to original element due to same number of electrons

physical properties of isotopes

affects mass, which affects melting/boiling points, and densities

core charge (definition)

force felt by the valence electrons towards the nucleus

core charge (pattern)

remains constant down the group, increases across a period

describe the pattern of core charge

number of protons increases as you move left to right

atomic radius

the distance from the nucleus to the valence electrons

describe the pattern of atomic radius

as you move across a period, core charge increases and radii decreases. electrons are held more tightly towards the nucleus.

ionisation energy

energy required to remove one electron from a neutral atom in a gas state

first ionisation energy (pattern)

increases across a period, decreases down a group

describe the pattern of first ionisation energy

decreases down a group due to shielding, increases across a period due to core charge

metallic character

tendency of an element to lose electrons and exhibit properties of metals, such as conductivity and malleability.

metallic character AND atomic radius

increases down a group, decreases across periods

electronegativity

tendency of atoms to attract electrons towards itself. strength depends on size of nuclear charge and radii

electronegativity (pattern)

decreases down a group, increases across a period

describe the pattern of electronegativity

decreases down a group as charge stays constant and number of shells increases. increases across a period as charge increases and pulls on the electrons stonger.

material

something which is classified as a pure substance or a mixture

element

substance which is made up of one type of atom and cannot be broken down

compound

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

molecule

when two or more atoms join together

what is the difference between a molecule and a compound?

a molecule can consists of same or different atoms, whereas a compound consists of different types of atoms.

mixture

contains 2 or more types of matter which are not chemically bonded

homogenous mixture

a mixture that has a uniform composition throughout

heterogenous mixture

a mixture that has an uneven composition

ionic bonding

when metals and non metals transfer electrons, resulting in ions that attract each other

properties of ionic bonding

brittle, high boiling/melting points, electrical conductivity

covalent bonding

when non-metals share electrons

properties of covalent bonds

usually low boiling/melting points, poor electrical conductivity, poor conductivity of heat, depends on shape of molecule

metallic bonding

a lattice of cations surrounded by a sea of delocalised electrons

delocalised electrons

electrons which are able to move freely in the lattice

why do metals have a high boiling point

the strong electrostatic attraction between the cations and delocalised electrons requires a large amount of energy to overcome

why are metals a good conductor of electricity

the sea of delocalised electrons provide free flow of electric charge and will flow towards a positive electrodee

how are metals malleable and ductile

due to the nondirectional bonding, allowing the layers of atoms to slide over another without breaking the entire bond

non directional bonding

where the forces between atoms do not have a specific direction, enabling atoms to rearrange without fracturing the material.

how are metals good conductors of heat

when an atom is heated, the electron gains energy and vibrates more frequently, being able to transmit energy rapidly through the lattice

alkane

saturated and cannot fit anymore H bonds

alkene

unsaturated and can fit more H bonds

substitution reaction

requires UV and occurs in alkanes or benzenes

addition reaction

this reaction breaks double bonds, is quicker, and occurs in alkenes

nanoparticle

an atom with a diameter between 1-100 nm

how is nanoparticle coating superior to corrosion?

as the coating provides a uniform layer, leading more particles to react with the surface.

endothermic reaction

occurs when more energy is required to break the bonds in the reactants.

exothermic reaction

occurs when more energy is released to create new bonds than to break the original bonds

biofuel

fuel derived from biological sources

fossil fuels

non-renewable source of energy formed from things in sediment

advantages of biofuels over fossil fuels

sustainable, less CO2 emission, less environmental destruction

advantages of fossil fuels over biofuels

cheaper, available everywhere