Reviewing the Periodic Table and other “Bohring” stuff from Grade Nine

Atomic Mass Definition: Atomic mass is the mass of an average atom of an element. Also equals the # of protons and neutrons in an atom.

Atomic number Definition: An atomic number is the number of protons in the nucleus of an atom. Atoms are neutral (no charge). So atomic number is also the number of electrons around an atom.

Setting the table Period: a horizontal row of elements on the periodic table. Group: (or “chemical family”) is a column of elements on the periodic table.

The Main Groups We will focus on five groups of elements: – IA (1) – The Alkali metals – IIA (2) – The Alkaline earth metals – VIA (16) – The Chalcogens – VIIA (17) – The Halogens – VIIIA (18) – The Noble gases

Periodic Patterns There are some important patterns on the periodic table. These patterns involve atomic structure. The period number tells us __________ The group number tells us __________

Patterns

Periodic Patterns The period number tells us how many electron shells an atom has. The group number tells us how many valence (outer) electrons the element has.

Periodic Patterns Metals, non-metals, and metalloids (semi- metals) show up in predictable places.

Metals, Non-metals, Metalloids

Atomic Structure We use the Bohr-Rutherford model. This model says atoms have: Dense, heavy nucleus of protons and neutrons. Spread-out, light electron cloud arranged into shells.

Bohr-Rutherford Model

Bohr Diagrams These show the number of protons and neutrons in the nucleus, and arranges the electrons into their shells.

Bohr Diagrams - Guidelines 1) Put the number of protons and neutrons in the middle (inside the nucleus) 2) The first electron shell can hold no more than two electrons. Fill it first. 3) Put electrons in the second shell. It can hold up to eight. 4) Put electrons in the third shell. It can also hold up to eight.

Patterns: Atomic Radius Atomic radius: the distance from the nucleus to the valence shell of an atom. Increases down a group. Decreases going right in a period.

Patterns: Atomic Radius

Patterns: Reactivity Metals can lose valence electrons. – Doesn’t take a lot of energy. This makes the atom a cation – a positively-charged ion. The bigger the atomic radius, the easier this happens. – “Bigger” metal atoms are MORE reactive!

Patterns: Reactivity

Non-metals can gain valence electrons. – Causes a release of energy. This makes an atom an anion – a negatively-charged ion. The smaller the atom, the easier this is. – “Smaller” non-metals are MORE reactive!

Patterns: Reactivity

Elements in the same group share chemical properties. This is due to having the same number of valence electrons.

Determining Atomic Makeup The periodic table can tell us what the atoms of any known element are made up of. This is determined from the atomic number and atomic mass.

Determining Atomic Makeup We know the total number of protons and neutrons. How can we figure out the number of neutrons, alone, that are in the atoms of a given element? We can subtract the number of protons (atomic number) from the number of protons and neutrons (atomic mass).

Determining Atomic Makeup Ex: Hydrogen Step 1: Look up the element on the periodic table. Step 2: Write down the equation – # of neutrons = atomic mass – atomic number Step 3: Write in the atomic mass (rounded to the nearest whole number) and atomic number for the element and solve. – # of neutrons for hydrogen = 1 – 1 = 0

Determining Atomic Makeup Ex: Hydrogen – Hydrogen has: 1 proton, 1 electron, and 0 neutrons. Ex: Aluminum Atomic number: 13 ( # of protons and electrons) Atomic mass: … ≈ 27 # of neutrons = atomic mass – atomic number = 27 – 13 = 14 neutrons Aluminum has 13 protons, 13 electrons, and 14 neutrons.

Lewis Dot Diagrams We can draw elements in a way that puts the focus on valence electrons – Lewis dot diagrams.

Lewis Dot Diagrams Method: 1.Write the symbol of the element (like Li, or B, or Ar). 2.Look up its group number on the periodic table. Determine how many valence electrons it has.

3.Starting on one side, draw dots representing valence electrons around the symbol. 4.Add a dot to each side of the symbol, one at a time, going in order. N

5.Stop adding dots once there are as many dots as there are valence electrons.

Ions: Metals lose valence electrons. – Forms a cation. To draw this: 1.Put the symbol in [brackets] 2.Write a number to show how many valence electrons were lost. 3.Place a + next to that number.

Example: Magnesium (normal) Magnesium cation [Mg] 2+

Non-metals gain valence electrons. – Forms anions. To draw this: 1.Surround the symbol with eight dots. – Non-metals want a full valence shell. 2.Surround everything in [brackets]. 3.Write a number to show how many valence electrons were gained. 4.Place a – next to that number.

Example: Phosphorus (normal) Phosphorus anion