Chemistry — The Periodic Table & Periodic Trends

What is the periodic table?

a model that organises the elements by increasing atomic number to reveal patterns in their properties

What three pieces of information does each box on the periodic table show?

the chemical symbol, the atomic number, and the atomic mass

What does an element's atomic number tell you?

the number of protons, which defines the element

What is an element's atomic mass on the table?

the weighted average mass of its naturally occurring isotopes

How are the elements ordered on the table?

by increasing atomic number

What are the three broad categories of elements?

metals, non-metals, and metalloids

Where are metals found on the periodic table?

on the left side, and they make up most of the elements

Where are non-metals found?

on the right side

Where are metalloids found?

in the zigzag region between the metals and non-metals

Give a few properties of metals?

shiny, solid, ductile, malleable, and good conductors of heat and electricity

What does ductile mean?

it can be drawn out into wires

What does malleable mean?

it can be hammered into thin sheets

Give a few properties of non-metals?

often brittle, dull, and poor conductors of heat and electricity

What are metalloids like?

in-between metals and non-metals, acting as semiconductors

What is a semiconductor?

something that conducts electricity better than a non-metal but not as well as a metal

Which metal is a liquid at room temperature?

mercury, an exception to metals being solid

What is a period on the periodic table?

a horizontal row

What is a group on the periodic table?

a vertical column

What happens to properties as you move across a period?

the atomic number rises and properties shift from metals to metalloids to non-metals

Why do elements in the same group behave similarly?

they have the same number of valence electrons

What are group 1 elements called?

the alkali metals

Give a few properties of the alkali metals?

soft, silvery, and very reactive

Why are alkali metals stored under oil?

they are so reactive they would otherwise react with air or water

Which group 1 element is an exception, and why?

hydrogen, which is actually a non-metal and behaves differently

What are group 2 elements called?

the alkaline earth metals

How do alkaline earth metals compare with alkali metals?

reactive but less so, and harder and denser

What are the middle-block elements called?

the transition metals

What are group 17 elements called?

the halogens

What are the halogens like?

highly reactive non-metals that form salts with metals

What are group 18 elements called?

the noble gases

What are the noble gases like?

almost completely unreactive

What does it mean for an atom to be reactive?

it readily loses, gains, or shares electrons to become stable

What does it mean for an element to be stable?

its electron arrangement does not typically change

What are valence electrons?

the electrons in an atom's outermost shell

Why do valence electrons matter most for reactivity?

they are the electrons lost, gained, or shared in reactions

Why are noble gases stable?

they already have a full outer shell of valence electrons

How many valence electrons make an atom stable?

eight, or two in the case of helium

Why is an atom with one valence electron reactive?

it readily loses that one electron to reach a stable full shell

Why is an atom with seven valence electrons reactive?

it readily gains one electron to complete a full shell of eight

How can you find valence electrons from the group number?

group 1 has 1, group 2 has 2, and groups 13 to 18 have 3 up to 8

What happens to valence electrons as you go down a group?

they stay the same, even though the total number of electrons rises

What happens to valence electrons across a period?

they increase from left to right