Download Goal 5 – Structure and Properties of Matter

Goal 5 – Structure and Properties of Matter
Many scientists have contributed to the different historical models of the atom.
John Dalton – claimed that the atom was a tiny, indivisible sphere, and that atoms of different elements has different masses and
combined in specific ratios to form compounds.
JJ Thomson – discovered that atoms contained both positive and negative charges, and that these charges proof that atoms could be
divided into smaller particles. Thomson said that the positive and negative charges were equal in quantity, and that the negative charges
were scattered about a positive fluid like blob.
Ernest Rutherford – conducted experiments to conclude that atoms have a dense positive centre, called a nucleus, and a less dense area
outside the nucleus, in which the electrons orbited much the same way that planets orbit the sun.
Niels Bohr – stated that electrons orbit the nucleus according to specific energy levels, and that there was a maximum number of electrons
that occupies each level. It was impossible to predict the exact location of an electron within an atom, but that it was more likely to occur
within a probable area called an electron cloud.
Atomic Structure – the three parts of an atom are the protons (+), neutrons and the electrons. Protons and neutrons are found in the
center of the atoms and account for most of the mass of the atom. Electrons take up most of the volume of the atom, as they orbit around
the nucleus, but account for very little of the mass.
The mass of a proton or neutron is equivalent to 1 atomic mass unit, and the sum of all the protons and neutrons in an atom is equal to the
atomic mass of the entire atom. Elements are made up of only one type of atom. Some atoms in the same atom may have different
masses. These atoms are called isotopes, and are different in mass because they have different numbers of neutrons in the nucleus.
The attraction of the electrons to the protons in the nucleus are what keep the electrons close to the nucleus. The repulsion of the protons
within the nucleus are overcome by the binding force that holds it together.
The atomic number of an element is the same as the number of protons and electrons within a neutral atom of that element.
Matter is anything that takes up space and has mass. All matter has both physical and chemical properties. Physical properties can be
observed using the 5 senses, and typically do not involve having to alter the matter in any way (ductility, density, lusture). Chemical
properties are normally only observed when the matter is chemically changed (flammability, reactivity).
The three phases of matter are solid, liquid and gas. As the energy of the particles within a sample of matter increase, the matter will
transition from one phase to the next. When a phase change is occurring, the temperature of the substance does not normally change.
Phase changes include melting, freezing, vaporization/condensation, sublimation and deposition.