A physical change is one in which altering the substance doesn’t change its composition. In other words, this is a change in the form of a substance without the production of a new substance. Physical changes can include breaking up the substance into smaller pieces or altering its state of matter.
A chemical change does involve a change in the substance’s composition. Here the change in the composition of a given substance causes a new substance to be produced in place of the original substance. Burning a match is an example of a chemical change.
Elements, which are listed in the periodic table of elements, are substances that can’t be broken down any further by ordinary types of chemical change.
Compounds consist of two or more elements that are combined chemically in such a way that the elements themselves can no longer be identified by their individual properties.
Mixtures consist of two elements mingled together without combining chemically. The individual properties of each material are maintained.
Shape Volume
Solid Definite (holds shape) Definite (fixed volume)
Liquid No definite shape (takes the shape of the container) Definite (fixed volume)
Gas No definite shape (takes the shape of the container) No definite volume (takes the volume of the container, but will expand indefinitely if not contained)
Atomic mass is generally equal to the sum of the number of protons plus the number of neutrons in an atom. This can be found in reference charts and on the periodic table, typically below the element’s chemical symbol.
Molecular mass is found by adding up all of the atomic masses of all of the individual atoms in one molecule of a compound.
Location Charge
Proton nucleus positive
Neutron nucleus no charge (neutral)
Electron shells (orbitals) surrounding the nucleus negative
Dalton’s atomic theory makes the following assumptions:
All matter consists of small particles called atoms.
All atoms of the same element are alike in size, shape, and mass, but differ in these properties from the atoms of the other elements.
Chemical reactions take place between atoms, and even in the most violent chemical reactions, the atoms don’t break into pieces.
Atoms combine with other atoms to form molecules.