Atomic structure, the periodic table, bonding, properties of matter Flashcards
what is a chemical bond?
a force of attraction
describe a covalent bond
pair of electrons are shared between non-metal atoms to gain full outer shells
what is the IMF between molecules in simple covalent substances?
weak
what is the usual state of simple covalent substances and why?
gases and liquids - IMF broken in state change
what is the BP of simple covalent substances?
low BP
what is the charge of simple covalent substances?
neutral charge (doesn’t conduct electricity)
what is the formula type used for simple covalent substances?
molecular
a bigger molecule has what type of IMF and MP?
stronger intermolecular forces - higher melting point
what is the state of giant covalent substances?
solids
what is the MP of giant covalent substances?
very high melting point
what is the atomic structure of giant covalent substances?
all atoms bonded to others by strong covalent bonds which must be overcome to boil/melt these substances
what is the formula type of giant covalent substances?
empirical
describe a metallic bond
- atoms in metals are tightly packed in layers - giant 3D lattices
- outer electron(s) from each atom is delocalised & is able to move through the structure
- each metal ions is equally attracted to delocalised electrons by electrostatic forces of attraction
describe an ionic bond
- metals react with non-metals
- electrons are transferred from the outer shell of metal atoms to the non-metal atoms, to get a full valence shell
- strong electrostatic force of attraction between oppositely charged ions
what are the properties of ionic substances?
- high melting points as there are strong forces between ions - lots of energy needed to break/overcome them
- solid at room temperature
- do not conduct electricity as solids
- conduct electricity when molten or in solution - as solid, ions in fixed positions and cannot move so cannot carry charge. when molten/dissolved, ions free to move & can carry charge
describe the structure of ionic compounds when dissolved in water
water causes the giant lattices to break apart so ions become individual and are free to move.
what are ions?
electrically charged particles with a different number of protons and electrons
why do metals form positive ions?
it is easy for them to lose electrons as they have a small number of electrons in the valence shell
what does ion charge correspond to?
group number (for 1=1+ 2=2+ 3=3+ 5=3- 6=2- 7=1-)
what is a pro of the dot-cross diagram?
shows the electron structure of the ions
what is a con of dot-cross diagram?
can give the impression that the structure is made of pairs of ions, rather than being a continuous structure containing a massive number of ions
what is a pro of the ball and stick structure?
helps to show how ions are arranged relative to each other
what are some cons of the ball and stick structure?
- the lines connecting ions may be confused with covalent bonds
- it may be thought that ions are far apart from each other
what is pro of the 3D space filling structure?
gives a very good representation to how ions are packed together
what is a con of the 3D space filling structure?
can give the impression that the structure is limited to a few ions rather than being a continuous structure containing a massive number of ions
what is a pro of the 2D space filling structure?
very easy to draw
what is a con of the 2D space filling structure?
- only shows the structure in 2D but the lattice is really 3D
- can give the impression that the structure is made of pairs of ions, rather than being a continuous structure containing a massive number of ions
what are the features of a solid?
- forces of attraction between particles are strong so particles are held in fixed positions (they do vibrate)
- particles do not move from fixed positions so keep a definite shape and volume
- the hotter they get the more they vibrate so solids expand slightly when heated
what are the features of a liquid?
- forces of attraction between particles are weak so particles are held close together but are in random positions and move
- definite volume but not shape
- particles move with random motion
- the hotter they get the faster they move so liquids expand slightly when heated
what are the features of a gas?
- forces of attraction between particles are very weak
- particles travel in straight lines until something changes their direction so will spread out
- do not keep definite volume or shape
- will expand to fill whatever container they are in.
describe the bonding in silicon dioxide
- strong covalent bonds between O and Si atoms
- each Si bonded to 4 O atoms
describe the bonding in diamond and carbon
- strong covalent bonds between all atoms (diamond, each is bonded to 4 others, graphite each is bonded to 3)
- both are giant covalent (graphite is in layers [malleable, as layers slide])
- very high M/BP due to strong covalent bonds
- graphite conducts electricity (each atom has spare delocalised electron, forms electron cloud, free to move throughout structure)
describe the structure of pure metals
arranged in layers - slide over each other - malleable
describe the conductivity of metals
good - delocalised electrons carry charge throughout structure
what is an alloy?
mixture of metals
why are alloys harder than pure metals?
atoms are different sizes which distorts regular lattice structure so layers cannot slide
what is the structure of graphene?
a single layer of graphite (1 atom thick)
what are the properties of graphene?
excellent conductor of electricity (delocalised electrons) and extremely strong
why is graphene strong?
each carbon atom is strongly bonded to 3 other carbon atoms by covalent bonds which require a lot of energy to overcome
what is the structure of buckminster fullerene
60 carbon atoms arranged in a hollow sphere - these form rings with 5 or 6 carbon atoms
describe the structure of fullerenes
molecules with hollow shapes, hexagonal rings of carbon atoms (can also be rings with 5 or 7 carbon atoms)
what are some uses of fullerenes?
pharmaceutical delivery, lubricants, catalysts
What are the features of carbon nanotubes?
high tensile strength and excellent conductors of heat and electricity
what does ‘nano’ mean?
1 * 10^-9
What are 3 applications of nanoscience?
- antibacterial bandages & surfaces using silver nanoparticles to inhibit microorganism growth
- gold nanocages; used for drug delivery to specific sites in the body
- carbon nanotubes; reinforce materials used for sports; more durable and water resistant
what are the features of nanoparticles?
- made of a few hundred atoms
- huge sa:v ratios so properties are different to behaviour on a large scale
- smaller quantities of nanoparticles are needed to be effective than materials with normal particles sizes due to high SA:V ratio
what is a risk of nanoparticles?
breathing them in may damage lungs
what was JJ Thomson’s model of the atom?
- plum pudding model
- ball of positive charge with negative electrons embedded in it
what happened in the alpha particle experiment?
- positive alpha particles fired at thin piece of gold
- most went through but some were deflected
- suggested the positive charge of an atom is confined in a small volume (nucleus)
in the gold alpha particle experiment, why did most alpha particles pass straight through gold atoms?
the atoms are not solid - mostly empty space
in the gold alpha particle experiment, why did most alpha particles pass straight through gold atoms?
some come into contact with the nucleus which is positively charged, so is deflected - same charges repel
what was Bohr’s adaptation to the model of the atom?
suggested electrons orbit nucleus at specific distances
what was Chadwick’s adaptation of the model of the atom?
suggested the nucleus also contained neutral particles
what are two key differences between thomson’s plum pudding model and rutherford’s replacement?
electrons in fixed orbit - shows protons in nucleus vs being a positive mass
what is atomic number?
total protons in an atom
what is mass number?
total protons and neutrons (bigger number)
what is the empirical formula?
simplest ratio of atoms in a compound
what is the molecular formula?
actual number of atoms in a compound
what is an allotrope?
the atoms of the same element are bound to each other in different ways - the spatial arrangement of atoms is different
what is an isotope?
members of a family of an element that all have the same number of protons but different numbers of neutrons
what is group 0?
noble gases
what are the properties of the noble gases?
- chemically inert, as have stable electron configurations (full outer shells)
- low density
- non-flammable
- generally low boiling point which increases down the group (as the atoms become larger so IMF become stronger, more energy is needed to overcome them)
- exist as single atoms
what is group 1?
alkali metals
what are the properties of the alkali metals?
- low density
- very reactive (1 valence electron)
- react with non-metals to form ionic compounds
- form compounds that are white solids
- dissolve in water to form colourless solutions
- become more reactive down group (outer shell further away from nucleus - weaker attraction)
what is group 7?
halogens
what are the properties of the halogens?
- non-metals
- diatomic molecules
- react with metals to form ionic compounds
- form molecular compounds with other non-metals
- form hydrogen halides
- less reactive going down group (outer shell is further from nucleus - electron gained less easily)
- melting and boiling points increase going down (as the atoms become larger so IMF become stronger, more energy is needed to overcome them)
what are the properties of the transition metals?
- good conductors of heat and electricity
- can be hammered or bent into shape easily
- high melting points (but mercury is a liquid at room temperature)
- usually hard and tough
- high densities
Gallium was discovered six years after Mendeleev published his periodic table. Give two reasons why the discovery of gallium helped Mendeleev’s periodic table to become accepted.
- it fitted in a gap Mendeleev had left
- its properties were predicted correctly by Mendeleev
compare group 1 and transition metal properties
- group 1 metals have lower mp/bp and densities, are more reactive, always form 1+ ions and white compounds, and react with water and oxygen
- transition metals have higher mp/bp and densities, are unreactive, form ions with different charges and coloured compounds, and are used as catalysts
NaCl is solid at RT with a high mp/bp whereas Cl2 is a gas at RT. Explain the difference in properties
- NaCl is an ionic lattice with strong electrostatic forces of attraction between each ion which require lots of energy to overcome
- Cl2 is a small molecule with weak IMF which do not require much energy to overcome
which 3 of the following substances have weak IMF?: CO2, CH4, graphite, graphene, diamond, O2
CO2, O2, CH4
Suggest one limitation of using a dot and cross diagram and one limitation of using a 3D diagram.
dot and cross diagram only shows how electrons are arranged and 3D diagram only shows the arrangement of ions in space
what was john dalton’s model of the atom?
tiny spheres that could not be divide
what was ernest rutherford’s model of the atom?
nuclear model
- the mass of an atom is concentrated at its centre, the nucleus
- the nucleus is positively charged
what was niels bohr’s model of the atom?
planetary model
- electrons orbit the nucleus in shells.
- The shells are at certain distances from the nucleus.
what was chadwick’s model of the atom?
- found evidence for the existence of particles in the nucleus with mass but no charge.
- These particles are called neutron
