The smallest particle of an element that retains the identity of the element.
Atoms are composed of protons, electrons, and neutrons.
The idea originally came from the Greeks which thought about the smallest piece of matter possible, they called this the atmos which means uncuttable.
A negatively charged particle within the atom. They have a very small mass about 1840 times less than that of a proton or neutron.
Electrons whiz around the atom in defined areas or energy levels.
A particle that is smaller than the atom.
E.g. protons, electrons, neutrons, photons, quarks, neutrinos, etc.
In chemistry, the positively charged centre of the atom.
A positively charged particle that is part of every atomic nucleus. Has almost the same mass as a neutron.
An uncharged particle that is part of almost every atomic nucleus. Has almost the same mass as a proton.
Fixed regions around the nucleus that electrons occupy. Electrons can move from to a higher energy level by absorbing a certain amount of energy. They can move down an energy level by releasing energy.
In the first energy level there is a maximum of two electrons. In the second and third there is a maximum of eight electrons.
The number of protons in the nucleus of an atom.
An atomic number identifies the atom as a particular element since if the number of protons changes, it has become a different element.
The sum of the number of protons and the number of neutrons in the nucleus of an atom.
The mass number is always a whole number since there can't be half of a proton or neutron.
One of two or more forms of an element that have the same number of protons but a different number of neutrons.
You denote an isotope by writing the name of the element, followed by a hyphen, and finally the number of protons and neutrons in the isotope.
E.g., hydrogen has two stable isotopes; hydrogen-1 or normal hydrogen, and hydrogen-2 or deuterium, hydrogen also has a radioactive isotope called hydrogen-3 or tritium.
A diagram of an atom that shows the number of protons and neutrons in the nucleus and the position of electrons in the energy levels.
The average mass of the naturally occurring isotopes of an element.
E.g., hydrogen has an atomic mass of 1.0, carbon is 12.0, chlorine is 35.5.
A system for organizing the elements into columns and rows, so that elements with similar properties are in the same column.
A Russian chemist names Dimitri Mendeleev organized the known elements of the 1860s into a table that would be later known as the period table. He placed gaps were the properties of elements didn't match up and this has proven to be very useful in guessing the properties of unknown elements.
Typically an element that is hard, shiny, malleable, ductile, is a good conductor of heat and electricity, and is solid at room temperature (except mercury).
E.g., copper, iron, tin, etc.
Typically an element that is not shiny, malleable, nor ductile, and is a poor conductor of heat and electricity.
E.g., fluorine, carbon, iodine, etc.
An element that shares some properties with metals and some properties with non-metals.
An example would be silicon which is conductive and shiny like metals, but also brittle like non-metals.
A horizontal row of elements in the periodic table.
The period also tells you how many energy levels there are, e.g., the elements in Period 2 have two energy levels.
A vertical column of elements in the periodic table.
Elements in the same group are also often called families since they have similar properties. E.g., all the elements in Group 17/halogens share the property of high reactivity.
The elements in Group 1 (except for hydrogen).
They have low melting points, are soft enough to be cut with a knife, and are highly reactive.
Alkaline earth metal
The elements in Group 2.
They are highly reactive (less so than the alkali metals), and if they are heated they will burn in air; this quality makes them useful in producing bright colours for fireworks.
The elements in Group 17.
They are highly reactive, extremely corrosive, and the melting points increase as you go down the group.
The elements in Group 18.
They are colourless, odourless, gases, and have extreme non-reactivity.
An electron in the outermost occupied energy level of an atom.
These electrons are very important when considering the reactivity of elements and what kinds of bonds they can form.
The noble gases are so non-reactive because they have a full set of valence electrons. On the other end of the scale there is the halogens and alkali metals that are so reactive because they are just one electron away from having a full set of valence electrons.