definitions Flashcards
(24 cards)
An atom is
the smallest part of an element that can exist as a stable entity
An ion is
a species with a positive or negative charge
An element is
a substance that contains only one type of atom
A compound is
a pure substance, which contains two or more different elements, chemically bonded together
A molecule is
the smallest part of an element or a compound, which can exist alone under ordinary conditions
A mixture is
two or more substances that can be separated by physical means
Proton (atomic) number is
equal to the number of protons in the nucleus of an atom
Nucleon (mass) number is
equal to the number of particles (protons and neutrons)
in the nucleus of an atom
Isotopes are
atoms of the same element, with the same number of protons but different number of neutrons
Radioactivity is
a nuclear change where energy is released as radiation and a new nucleus is formed with a different proton number
Elements:
They are made up of the same type of atom. They cannot be broken down into simpler chemicals
Diffusion
is the spreading of one substance through another from a region of high concentration to a region of low concentration due to the continuous random motion of particles
A macromolecule
consists of a large number of atoms bonded together to form one molecule with a very high relative molecular mass (Mr)
Allotropes
are different crystalline forms of the same element. They have the same chemical properties, but different physical properties
Metallic bonding
is the strong non-directional electrostatic force of attraction between the lattice of positive ions and the mobile ‘sea’ of valence electrons in a 3-dimensional structure
Ar
is the mass of one atom of an element relative to one twelfth of the mass of one atom of 12C
Mr
is the sum of the relative atomic masses of all the atoms in one molecule of the compound
Melting point
the temperature at which a pure solid changes to a liquid without a change in temperature.
Condensation point
the temperature at which vapour changes to a liquid without a change in temperature
Boiling point
the temperature at which a pure liquid changes to vapour without a change in temperature
Solidifying point/freezing point
the temperature at which a pure liquid changes
to a solid without a change in temperature
Evaporation
when liquids change into gases over a range of temperature below the boiling point.
Sublimation
where a solid changes straight to a gas, without changing to a liquid, or a gas changes to a solid without changing to a liquid.
A volatile liquid
a liquid that easily turns into a gas as it has a low boiling point (close to room temperature).
