atomic structure and bonding Flashcards
define what an atom is
the smallest particles of matter that cannot be broken down any further
what particles are in the nucleus
protons and neutrons
what is the mass of an atom measured in
atomic mass units
which of the three is the lightest particle
electrons
mass of protons
1 unit
mass of electrons
almost nothing
mass of neutrons
1 unit
where is the mass number on the symbol of an element
on the top
where is the proton number on the symbol of an element
on the bottom
how can you identify an atom using protons
by the number of protons
another name for proton number
atomic number
why do atoms have no charge
because they contain the same number of proton and electrons
define mass number
to total number of protons and neutrons in an atom
another name for mass number
nucleon number
do ions have electronic charge
yes
why are ions charged
ions gain and lose electrons. when they gain an electron they become negatively charged. when they lose an electron they become positively charged. (the number of protons does not change)
why do atoms form ions
because they gain or lose electrons to obtain a stable outermost shell
define ‘isotopes’
atoms of the same element that have a different neutron number but same proton number (have different nucleon number)
what are the 2 types of isotopes
stable and unstable isotopes
why are some isotopes unstable
because the the extra neutrons are radioactive
what are unstable isotopes called
radioisotopes
why are radioisotopes radioactive
because the nucleus is unstable. the atoms naturally will break down or decay giving out radiation in the form of particles and rays, plus a large amount of energy.
define relative atomic mass
the average mass of a large number of atoms of an element
what is the symbol for relative atomic mass
Ar
what is the standard used for the Ar scale
carbon-12
what is the Ar formula
avg. mass of isotopes of an element/ 1/12 x mass of 1 atom of carbon 12
which electron shell has the highest energy level
the outermost electron shell
what is another name of the outer- shell electrons
valency electrons
why don’t unreactive atoms form bonds
because they have a stable arrangement of electrons in their outermost shell which does not allow them to bond with other atoms
why do atoms form bonds
to gain a stable outermost electron shell
define an ionic bond
a chemical bond between a metal and non-metal
how do solid ionic compounds formed
the form a lattice of alternation positive and negative ions that are held together by strong ionic bonds
define ‘lattice’
the arrangement of atoms
why don’t group 4 and 5 elements use ionic bonds
because they have to gain or lose to many electrons and it take too much energy.
what are compound ions
ions formed from a group of bonded atoms.
define covalent bonds
a bond where atoms share the electrons in their outer energy levels. this occurs between non-metal atoms.
define ‘molecule’
a group of atoms held together by covalent bonds.
what are elements made up of molecules called
molecular element
define ‘diatomic’
elements made up of molecules containing two atoms.
define a single bond
when atoms share one pair/2 electrons
single bond symbol
element-element
eg: (CI-CI)
define a double bond
when atoms share two pairs/4 electrons
double bond symbol
element=element
eg: (O=O)
define a triple bond
when atoms share three pairs/6 electrons
triple bond symbol
elementΞelement
eg: (NΞN)
why do ions have high melting and boiling points
because ionic bonds are very strong and it takes a lot of heat energy to break up the lattice. ions also have double the charge so its ionic bonds are stronger.
why are ions soluble in water
water molecules are able to bond with both the positive and the negative ions, which breaks up the lattice and keeps the ions apart.
what is the term for an element that has been dissolved in water
aqueous
define ‘molten’
a substance or element in liquid form
why can ions only conduct electricity in molten or aqueous form
because the ions become free to move and since they are charged, they can then conduct electricity. (they also gain more charge from the water molecules)
why do covalent compounds have low melting and boiling points
because the attraction between the molecules is low. so it does not take much energy to break up the lattice and separate them from each other.
why are many molecular compounds liquids or gases at room temperature
because they have low melting and boiling points.
why are many covalent liquids volatile
because the attraction between the molecules are low.
define ‘volatile’
evaporates easily
why can’t covalent compounds conduct electricity
because covalent compounds have no charged particles.
what are the 2 types of molecular structures
simple molecular or giant molecular
define a simple molecular structure
formed from only a few atoms and have strong covalent bonds between the atoms within a molecule.
define inTRAmolecular bonds
strong covalent bonds between the atoms within a molecule.
define inTERmolecular bonds
weak bonds between the molecules.
why do some covalent compounds have high melting and boiling points and strong inTERmolecular bonds.
because they have strong lattice structures and is held in place by 4 strong covalent bonds
what are structures like diamonds and silica known as
giant covalent structures or macromolecules.
why are diamond very hard
because each atom is held in place by four strong covalent bonds.
why can’t diamonds conduct electricity
because there are no ions or free electrons to carry the charge.
define ‘allotropes’
two forms of the same element.
why are diamond and graphite so different
because the they have very different structures. (graphite’s structure is a ring of 6 atoms that form flat sheets that lie on top of each other, held together by weak forces)
why is graphite so soft and slippery
because the sheets
can slide over each other easily.
why can graphite conduct electricity but not diamond
because each carbon atom has four outer electrons, but forms only three bonds. so the fourth electron is free to move through the graphite, carrying charge.
define ‘metallic bonding’
when the negatively charged electrons attract all the positive metal ions and bond them together with strong electrostatic forces of attraction as a single unit.
how does metallic bonding work
electrons in the outer energy level of the atom of a metal move freely throughout the structure they are delocalised forming a mobile ‘sea’ of electrons.
why do metals have high melting points
because it takes a lot of heat energy to break up the lattice, formed by its strong metallic bonds.
define ‘malleable’
it means they can be bent and pressed into shape.
define ‘ductile’
it means they can be drawn out into wires. this is because the layers can slide over each other.
why are metals good conductors of heat
because the free electrons take in heat energy, which makes them move faster. they quickly transfer the heat through the metal structure.
why are metals good conductors of electricity
because the free electrons can move through the lattice carrying charge.
