SC1: key concepts in chemistry Flashcards
mnemonic for diatomic elements
I Bring Clay For Our New House:
iodine, bromine, chlorine, fluorine, oxygen, nitrogen, hydrogen
compound
a chemical combination of two or more elements
what does a chemical formula show?
how many atoms there are in each element of a compound
what is a covalent bond?
a chemical bond formed when two or atoms share electrons
what are covalent bonds between?
non-metals
what is an ionic bond?
formed when one or more electrons are transferred from one atom to another
what are ionic bonds between?
metals and non metals
what is an ion?
the charged particle formed when an atom loses or gains electrons
what happens in a chemical reaction?
the atoms of ions in reactants separate from one another and join back together in a different way to form products
what is an aqueous solution?
a solution in which water is the solvent
what is a precipitation reaction
when two soluble substances react together to make a product which is insoluble (the precipitate)
how is a precipitation reaction modelled?
with a balanced ionic equation
what are spectator ions?
ions that do not participate in a reaction
what is a hazard?
something with the potential to cause harm
what is a risk?
the chance that a hazard will cause harm
what is a precaution?
something that can be done to reduce a risk of harm
what is a risk assessment?
something that describes the hazards and risks of harm & what precautions are needed to work safely
what is the order of atomic structure discovery?
- john dalton
- j.j thompson
- ernst rutherford
- niels bohr
- james chadwick
john dalton
-atoms can’t be broken
-there is nothing smaller than an atom
j.j thompson
-discovered the electron (1904)
-atoms made up of small, negatively charged atoms in a positively charged area
-plum pudding model
ernst rutherford
-discovered the nucleus in 1909
-fired alpha particles (positively charged) at a thin gold lead in a vacuum, most passed through, a few were deflected, some came back
-small positively charged nucleus surrounded by empty space, electrons orbited nucleus
-nucleus was heavier than could be explained with only protons so ernst proposed neutrons
-ernst couldn’t explain why electrons didn’t collapse into the nucleus
niels bohr
-1913: discovered that electrons move around the nucleus in orbits called electron shells
-worked with rutherford
-rutherford-bohr model was supported by scientists
what happens when atoms absorb energy?
their electrons move to higher energy levels
mass of an electron
1/1835
what is atomic mass?
protons + neutrons + electrons
what is an atomic number?
the number of protons/electrons in an atom
what are isotopes?
atoms of the same element with different numbers of neutrons
what is RAM?
relative atomic mass
RAM facts
-not whole numbers
-mean relative mass of atoms of different isotopes in an element
what is the formula for RAM?
(% of isotope 1 × mass of isotope 1) + (% of isotope 2 x mass of isotope 2) / 100
mendeleev’s periodic table
-arranged by increasing atomic mass
-put similar properties below each other in groups
- left gaps for yet to be discovered elements
-looked at the chemical and physical properties of the elements next to a gap to predict the properties of these undiscovered elements
modern periodic table
-arranged by increasing atomic number
-rows = periods
-columns = groups (elements w similar
properties)
-metals on left side, non-metals on right
what is electron configuration?
the arrangement of electrons in an atom
how is electron configuration linked to an elements position on the periodic table?
-the number of shells is the period the element is in
-the number of electrons in the outermost shell is the group number of the element
-the number of electrons in all shells is the elements atomic number
why do elements in the same group have similar properties?
they have the same amount of electrons in their outer shell, when atoms collide & react, the outer shells interact, so because they have the same amount of electrons in their outermost shell, they have similar properties
valency
equal to the number of electrons that each atom needs to gain, lose or share to fill its outer shell
what is an ion?
an atom that has lost or gained electrons to obtain a full outer shell
what is an ionic compound?
a compound that consists of positive and negative ions
anion
negative ion
cation
positive ion
dot and cross diagram
a drawing to show only the arrangement of electrons of the atoms or bonding of a simple molecular structure
ionic lattice
regular repeating arrangement of particles
why is an ionic lattice formed?
the positive and negative ions attract one another and form a regular pattern with oppositely charged ions next to eachother
why do solid ionic compounds form crystals?
the lattice arrangement continues in three dimensions
what is an ionic lattice held together by?
ionic bonds
what direction(s) do ionic bonds act in?
any direction
naming ionic compounds
ide = 2 elements
ate = 3 or more with one oxygen
why do ionic compounds have high melting and boiling points?
because of the strong electrostatic attraction between ions, it takes a lot of energy to overcome this attraction and break the many strong bonds to melt or boil the compounds
why do ionic compounds conduct electricity only when molten or aqueous?
the ions are free to move and carry charge
polyatomic ion
an ion made of two or more atoms
covalent bonds
bonds created by sharing electrons with other atoms
molecule
a group of atoms bonded together covalently
what will molecules of the same element and compound always have?
a set size
simple molecule
molecule made up of a small number of atoms held by covalent bonds
why can’t atoms and molecules be seen with light microscopes?
they’re too small
why do simple molecular substances have low melting and boiling points?
there are weak intermolecular forces between the molecules that do not require much energy to overcome
why can’t simple molecular substances conduct electricity?
they have no charge
what are giant covalent bonds?
many atoms joined by covalent bonds
why do giant covalent bonds have a high melting and boiling points?
lots of energy needed to overcome strong bonds
why aren’t giant covalent bonds electric conductors?
they have no charge
why are giant covalent lattices insoluble?
the covalent bonds are far too strong to be broken by interaction with solvents (a substance can dissolve with water if it forms enough attractions with water molecules
diamond (giant covalent lattice, form of carbon)
-each carbon atom joined to four other carbon atoms by covalent bonds
-no free electrons
-tetrahedral structure
what are the properties of diamonds?
-diamonds are very hard due to the rigid structure of the carbon atoms held together by covalent bonds
-doesn’t conduct electricity
-high melting point
what can diamonds be used for?
cutting tools
graphite (giant covalent lattice, form of carbon)
-each carbon atom is joined to three other carbon atoms by covalent bonds
-hexagon layered network structure
-the layers have weak forces between them & can slide over one another
-each carbon atom has one un bonded outer electron which is delocalised
properties of graphite
-can conduct electricity due to the delocalised electron
-slippery due to the weak forces
uses of graphite
-lubricants
-pencils
-electrodes in batteries
graphene (form of carbon)
structure resembles single layer of graphite
properties of graphene
-high melting point & strong bc of regular arrangement of carbon atoms joined by covalent bonds
-conduct electricity well due to delocalised electrons
fullerene (very large molecule)
a molecular form of carbon that consists of atoms arranged in the shape of a hollow sphere
what are two fullerenes?
-nanotubes
-buckyballs
nanotubes
resembles a layer of graphene, rolled into a tube shape
properties of nanotubes
-high tensile strength, as in the tension that can be withstood without breaking
-conduct electricity due to delocalised electrons
-strong
buckyballs
spheres or squashed spheres of carbon atoms
properties of buckyballs
-slippery as there are weak intermolecular forces between buckyballs
-lower melting points than graphite or diamond
metals properties
-shiny
-high melting points and densities,
-malleable (can be shaped without breaking)
-high density (high mass for its size)
-ductile (can be drawn into a long wire without snapping or breaking)
-good electric & heat conductors (delocalised atoms can move through the lattice structure & form an electric current)
where are metals located on the periodic table?
left
where are nonmetals located on the periodic table?
right side
metal structure
positive ions in a sea of delocalised electrons
non metal properties
-dull
-brittle (shatter when hit)
-poor electric & heat conductors
- low melting points
relative formula mass
the sum of the relative atomic masses of the elements as given in the formula
empirical formula
the simplest whole number ratio of atoms
calculating empirical formula
- write out element symbols
- write out the mass/percentage of each element
- write Mr values
- divide masses by Mr
- divide by smallest number
- multiply (if needed) for integers
- write formula
law of conservation of mass
atoms aren’t created or destroyed in a chemical reaction, they join together differently than before the reactions to form products, this means that the total mass stays the same
reactions in a closed system
no substance enters or leaves, mass stays same
reactions an non enclosed system
-substances can enter or leave
-if a gas escapes, the total mass will look as if it has decreased
-if a gas is gained, the total mass will look as if it has increased
-the total mass stays the same if the mass of the gas is included.
concentration formula
mass of solute/volume of solvent
concentration
how much solute is dissolved in a solvent
mass formula (moles)
mass = mr x moles
when does a reaction finish?
when one of the reactants is all used up
what is a limiting factor in a reaction?
a reactant that is used up first in a chemical reaction
what does the mass of the product formed in a reaction depend on?
the limiting reactant, this is because no more product can form when the limiting reactant is all used up
