mod 1 Flashcards
what are the properties of a mixture?
- can be separated by physical means
- composition varies
- set of properties varies
- comprises two or more pure substances
- made of different types of particle groups
what are the properties of a pure substance?
- can’t be separated by physical means
- constant/definitive composition
- fixed set of properties
- made of one type of particle group
- can be separated by chemical means
homogenous
- uniform in all parts
- one visible layer
examples of homogenous
milk, coins, drill bits
what is a metal alloy?
solidified metal mixture that had other elements dispersed through it when molten
examples of alloys
steel –> iron & carbon
bronze –> copper & tin
brass –> copper & zinc
solder –> lead & tin
solution
solute dissolved in a solvent
- only one layer
- clear/transparent
- aqueous solution referent a solute dissolved in water
- non-aqueous solution doesn’t have water as a solvent
colloid
large molecules are evenly spread out through another substance, usually in a liquid the large molecules do not settle over time
- only one layer
- opaque/translucent
heterogenous
- not uniform in all parts
- more than one visible layer
suspension
mixture where combined substances do not dissolve in one another but form layers quickly
- two or more layers of substances
- may be clear translucent/opaque
examples of homogenous mixtures
alloy, solution, colloid
element
made of one type of atom in particle groups
compound
- made of two or more different types of atoms in each particle group
- made of two or more elements chemically joined
some useful mixtures
ores, saline solution
ores
rocks which contain a high enough content of a metal to make extraction of the metal profitable
- hematite –> iron oxide –> iron
- bauxite –> aluminium oxide –> aluminium
percentage of composition of mixture
% composition by mass = mass of substance / mass of mixture x 100%
what are separation techniques by particle size?
- sieving
- filtration
what is sieving?
using a metal net, separating the particles from larger particles e.g. gravel from sand
what is filtration?
uses a special membrane with fine holes allowing liquids through but not undissolved solids
what are separation techniques by density?
- sedimentation
- separating by funnel
what is sedimentation?
allows time for denser undissolved solids to settle to the bottom of a container
what are separation techniques by boiling point?
- evaporation
- distillation
what is evaporation?
uses heat to boil off the liquid part of a solution, leaving the solute behind
what is distillation
is evaporation with an added stepp to capture and condense the boiled liquid in a second chamber
what are elements made of?
made of one atom in each particle group
what is a molecule?
A molecule is two or more atoms connected by chemical bonds, which form the smallest unit of a substance that retains the composition and properties of that substance
what is a lattice?
a regularly repeating arrangement of atoms in three dimensions
how can you classify elements?
- physical properties
- chemical properties
what physical properties can elements be classified by?
- lustre
- melting & boiling point
- malleability
- ductility
- electrical conductivity
- heat conductivity
- density
what chemical properties can elements be classified by?
- ability to react with acid
- the ability to react with oxygen in the air
- ability to react with water
what is an atom?
- the smallest particle matter that exists by itself in nature
- the smallest unit of an element that has all the properties of that element
what is the basic structure of an atom?
made of three subatomic particles, proton, neutron and electron
- proton = + charge
- neutron = neutral charge
- electron = - charge
in the core protons and neutrons are grouped together, and electrons move around the nucleus at high speed in an electron configuration
what are isotopes?
atoms of the same element can have a different number of neutrons
what does the bohr model of the atom tell us?
- electrons can only move with a fixed amount of energy
- electrons with the same energy level move in the same orbit
- orbits closer to the nucleus contains lower energy
- each energy level has a max. no. of electrons
mass of atom = ?
= mass of protons + mass of neutrons
avg. atomic mass?
mass no. + mass no. / amount of elements
what is periodicity?
refers to the pattern of similar properties recurring at intervals when examining elements in increasing atomic number
what are the trends in electron configuration?
- elements in the same group have similar electron configurations
- more energy down a group
- different sub-shells are filled going across a period
what is the core charge of an atom?
core charge = no. of protons - no. of electrons in inner shell
what are the trends in atomic radius?
- decreases across the period because core charge increases and pulls each valence electron closer to the nucleus
increases down a group because the effect of the core charge is reduced
what is ionisation energy?
refers to the amount of energy required to dislodge an electron from an energy shell of a gaseous atom
what are trends for ionisation energy?
increases across a period and decreases down a row
increases across - increase in core charge
decreases down - electron is further from the nucleus so less tightly held
what is electronegativity?
is the ability of an atom to attract an electron into its valence shell
what are trends of electronegativity?
increases as you move from left to right across a period and decreases as you move down a group.
what are the trends in reactivity with water?
Down a group the reactivity of metals increases because it is easier for a metal atom with greater number of shells to lose electrons. Across a group the reactivity of metals decreases because the increasing core charge makes it more difficult for a metal atom to lose electrons.
what does melting point & boiling point indicate?
indicators of the strength of the bonding between particles or particle groups in a substance
what is ionic bonding
- An ionic bond is a type of chemical bonding that occurs between a cation and an anion.
- To form ions, which are charged particles, there is a transfer of electrons.
- It results in one atom positive and the other negative.
what is covalent bonding
- Covalent bonding occurs when two non-metal atoms share electron to gain a full outer shell which will make the atom achieve a stable electron configuration.
- There can be single, double or triple bonds.
electronegativity and bonding
- polar covalent bond, difference in electronegativity of 1.0 - 1.7, which is where they share electron unequally
- ionic bond, difference in electronegativity >1.7, the atom takes the electrons
- non-polar covalent bond similar electronegativity, this is when electrons are shared
what are the shapes of molecules useful for?
Molecular shapes are crucial for understanding covalent molecular substances’ properties like melting point, boiling point, hardness, and solubility, as they determine how molecules interact
what is the VSEPR model?
Valence Shell Electron Pair Repulsion Theory is used to determine the shape of small molecules.
what are non-polar molecules?
- A non-polar molecule is a molecule that does not have electrons due at just one end of the molecule.
- The electrons are spread out evenly making it an even distribution of charges and neutral overall.
what are polar molecules?
- A polar molecule is when one end of the molecule is slightly positive and the at the other end is slightly negative.
- A polar molecule is still neutral overall but has an uneven distribution of charges
what is a dispersion force?
Dispersion forces are attractions between non-polar molecules due to temporary dipoles caused by electron movement. They’re weak but always present, and strengthen with larger molecule size because more electrons can create temporary dipoles.
what are dipole-dipole forces?
Dipole-dipole forces occur in polar molecules due to attraction between positive and negative ends. They’re weak because partial charges are small but permanent.
what is hydrogen bonding?
Hydrogen bonding is a special type of dipole-dipole attraction between molecules, not a covalent bond to a hydrogen atom. It results from the attractive force between a hydrogen atom covalently bonded to a very electronegative atom such as a N, O, or F atom and another very electronegative atom.
