Yr9-C2: The periodic table:

John Newlands

English Analytical Chemist in the 1800s who arranged the elements on the periodic table by their atomic mass and called this arrangement the Law of Octaves.

Dmitri Mendeleev

Russian Chemist in the 1800s who arranged the elements known at the time in order of atomic mass and left spaces in his periodic table for undiscovered elements.

Electron Shells

The regions surrounding the nucleus of an atom where electrons are found. Shell 1 holds a maximum of 2 e–, Shell 2 holds a maximum of 8 e–, Shell 3 holds the next 8 e–, and Shell 4 holds the next 2 e–.

Alkali Metals

Group 1 elements on the periodic table that have 1 electron in their outer shell, are soft metals, have low melting points, low density, and are very reactive.

Halogens

Group 7 elements on the periodic table that are poisonous non-metals, have low melting and boiling points, and are highly reactive as they need to gain 1 more electron to achieve a full outer shell.

Physical Property

Any characteristic that can be determined without changing the substance's chemical identity, such as color, density, hardness, and melting and boiling points.

Chemical Property

Any characteristic that can be determined only by changing a substance's molecular structure, such as flammability, toxicity, acidity, reactivity, and heat of combustion.

Reactivity Trend in Group 7

The reactivity of elements in Group 7 decreases as you go down the group because the atoms get bigger, making it harder for the atom to gain one electron in its outermost shell.

Transition Metals

A collection of elements in the center of the periodic table, between Group 2 and Group 3, that can be used as catalysts in certain reactions and have different numbers of electrons on their outer shells, allowing for the formation of different ions and charges.