Chemistry Patterns (OCR)

Dmitri Mendeleev

He developed the periodic table in 1869 by organizing the elements based on atomic mass and observed elements with similar properties occurred at regular intervals.

Henry Moseley

In 1913 he rearranged the periodic table according to atomic number instead of atomic mass, resolving some inconsistencies in Mendeleev’s table.

Periodic Law

This law states that the properties of elements recur periodically when they are arranged by increasing atomic number.

Groups

It is the vertical columns in the periodic table, with elements in the same group sharing similar chemical properties because they have the same number of valence electrons.

Periods

Horizontal rows of the periodic table, which represent the filling of electron shells. Properties change across a period due to the increasing nuclear charge.

Periodic Trends

It is the patterns in the properties of elements that are based on their position on the periodic table.

What will be the periodic trend if you move from left to right?

atomic size decreases, ionization energy increases, and electronegativity increases

What will be the periodic trend if you move down a group?

atomic size increases, ionization energy decreases, and electronegativity decreases

Protons

have a positive charge (+1) and are located in the nucleus of the atom

Neutrons

have no charge (neutral) and are also found in the nucleus

Electrons

have a negative charge (-1) and are found in electron shells outside the nucleus

Electron configuration

it is the arrangement of electrons around the nucleus of an atom, detailing how electrons are distributed across different energy levels and orbitals

Effective nuclear charge (Z_eff)

it is the net positive charge felt by an electron in an atom

What is the formular of Effective Nuclear Charge?

What will be the periodic trend in terms of atomic radius if you move across a period?

the atomic radius decreases because the number of protons increases which pulls the electrons closer to the nucleus, reducing the size of the atom

What will be the periodic trend in terms of atomic radius if you move down a group?

the atomic radius increases because new electrons are further from the nucleus and experience more shielding from inner electrons

Ionization energy

it is the energy required to remove one mole of electrons from one mole of gaseous atoms

What will be the periodic trend in terms of ionization energy if you move across a period?

Ionization energy increases due to the increased nuclear charge and smaller atomic radius

What will be the periodic trend in terms of ionization energy if you move down a group?

Ionization energy decreases because the outer electrons are further from the nucleus, and there is greater shielding from inner electrons.

Formula for First Ionization Energy

Electronegativity

it is a measure of an atom's ability to attract and bond with electrons

What will be the periodic trend in terms of electronegativity if you move across a period?

Electronegativity increases because atoms are smaller and the nuclear charge is stronger, so they attract electrons more strongly

What will be the periodic trend in terms of electronegativity if you move down a group?

Electronegativity decreases because atoms are larger and the outer electrons are further from the nucleus, leading to weaker attraction for bonding electrons

Ionic bonds

it is formed when one atom transfers an electron to another, typically between a metal and a nonmetal.

What are the properties of Ionic bonding?

• High melting/Boiling points

• Conducts electricity in molten or dissolved fom

• Brittle structure

Covalent Bonding

it is formed when two nonmetal atoms share one or more pairs of electrons to achieve a full outer shell of electrons

What are the properties of covalent bonding?

• Low melting/boiling points

• Poor electrical conductivity

• Solubility in non-polar solvents

Metallic bonding

positive metal ions are held together by the attraction to the delocalized electrons

What are the properties of metallic bonding?

• Good conductors of electricity

• Malleable and ductile

• High melting/boiling points

Transition metals

it is metals with partially filled d-orbitals. They are typically harder, stronger, and more conductive than the main group metals.

Ligand

 is a molecule or ion that donates a pair of electrons to the metal ion

Reactivity series

arranges metals by their reactivity with water, acids, and other substances

Alkali metals

it is very reactive, electropositive, monovalent metals forming strongly alkaline hydroxide

Halogens

are highly reactive non-metals that tend to form salts with metals

Noble gases

these are inert because they have a full outer electron shell, making them chemically stable and unlikely to form compounds