Junior Cert Science: Atoms and the Periodic Table

Atom

Smallest particle of an element

Protons (p+)

Subatomic particles located in the nucleus of the atom with a positive charge (+1) and a mass of 1 atomic mass unit (amu).

Neutrons (n)

Subatomic particles located in the nucleus of the atom with no charge (neutral) and a mass of 1 atomic mass unit (amu).

Electrons (e-)

Subatomic particles located in orbitals or energy levels around the nucleus with a negative charge (-1) and a very small mass (negligible compared to protons and neutrons).

Atomic Number

The number of protons in an atom, the number of protons equals the number of electrons

Mass Number

The total number of protons and neutrons in an atom, calculated as , Number of Protons + Number of Neutrons.

Electronic Configuration

Describes how electrons are arranged in an atom, following the Aufbau principle where electrons fill the lowest available energy level first.

1st shell

Can hold 2 electrons.

2nd shell

Can hold 8 electrons.

3rd shell

Can hold 8 electrons.

Periodic Table

A chart that organizes all known elements according to their atomic number, electronic configuration, and recurring chemical properties.

Groups

The vertical columns of the periodic table where elements have similar chemical properties due to the same number of valence electrons.

Periods

The horizontal rows of the periodic table where elements have the same number of energy levels or shells.

Alkali Metals (Group 1)

Includes lithium (Li), sodium (Na), potassium (K), etc., characterized by being very reactive, having 1 electron in their outer shell, low melting and boiling points, and being soft.

Alkaline Earth Metals (Group 2)

Includes beryllium (Be), magnesium (Mg), calcium (Ca), etc., characterized by being less reactive than alkali metals and having 2 electrons in their outer shell.

Halogens (Group 17)

Includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At), characterized by being very reactive non-metals with 7 electrons in their outer shell.

Noble Gases

Includes helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn).

Properties of Noble Gases

Inert gases, meaning they are very unreactive.

Noble Gases Electron Configuration

Have 8 electrons in their outer shell (except for helium, which has 2).

Transition Metals

Includes iron (Fe), copper (Cu), zinc (Zn), gold (Au), and silver (Ag).

Properties of Transition Metals

Good conductors of heat and electricity.

Transition Metals Melting and Boiling Points

Have high melting and boiling points.

Transition Metals Compounds

Often form coloured compounds.

Uses of Transition Metals

Used in construction, electronics, and jewelry.

Ionic Bonding

Occurs between a metal and a non-metal.

Covalent Bonding

Occurs between two non-metals.

Example of Ionic Bonding

Sodium chloride (NaCl) - sodium (Na) gives up an electron to chlorine (Cl), forming oppositely charged ions that attract each other.

Example of Covalent Bonding

Water (H₂O) - oxygen shares electrons with two hydrogen atoms.