The Atom • Three basic components of an atom: • Electrons • Protons • Neutrons • An atom is mostly empty space, with almost all of the mass contained in the nucleus • Protons and Neutrons are contained in the centre of the atom known as the nucleus. • Electrons “orbit” the nucleus.
Parts of the Atom • Neutron: Large with no charge (n0) • Proton: Large with a positive charge (p+) • Electron: Small with a negative charge (e-) • Charge on an electron is equal and opposite to the charge on a proton • All elements (in their ground state) are neutral, meaning the number of protons and the number of electrons are equal.
Representing Elements • To represent elements we use the symbol A X Z • X – Atomic symbol • Z – Atomic number (p+) • A – Mass number (p+ + n0)
Example • Na Sodium • Atomic Number = 11 11 protons • Mass Number = 23 23 - 11 = 12 neutrons • Neutral # electrons = # protons = 11 23 Na 11
Periodic Table • 118(?) Elements are arranged in Groups (columns) and Periods (rows) • There are three types of elements: • Metals • Metalloids • Non-Metals • Periodic Table is broken into sections for each type
Patterns and Trends Metals Metalloids Non-Metals Elements that border the “staircase” tend to have both metal and non-metal properties. These elements are known as metalloids.
Electron Configurations • Electrons “orbit” the nucleus in regions known as shells. • The elements in the first period have one shell and each period adds another. • The first shell can only hold 2 electrons and each shell after that can hold 8 electrons. • When a shell is full move on to the next one.
Outer Shell/Electrons • The outer most shell of an electron configuration is known as the valence shell. • Electrons contained in this shell are known as valence electrons. • What do you notice about elements of the same group and the number of electrons in the outer most shell?
Period Table and Configurations • Period determines the number of shells and the group determines the number of valence electrons. • When looking at chemical similarities in the periodic table we look at the groups and not the periods.
Common Names of Groups • Group 1 (1A) – Alkali Metals • Group 2 (2A) – Alkaline Earth Metals • Groups 3-12 are called the transition metals • Groups 1,2,13-18 are called representative elements
Common Names of Groups • Group 17 (7A) – Halogens • Means “salt former” • Group 18 (8A) – Noble Gases • Only for first six periods. • Called Noble Gases because they don’t easily react with the other elements (full valence shell)
Isotopes • Isotopes are variations of the element where neutrons are added or removed to give different types (weights) of atoms. • Still the same element just different mass number. • Atomic number does not change so there is still the same number of protons present. • The atomic mass seen on the periodic table is the average mass of all the isotopes of that element.
Isotope Example (Hydrogen) 0 neutrons 1 neutron 2 neutrons • 2H and 3H are known as deuterium and tritium. • Also called “heavy” hydrogen
Lewis Dot Diagrams • Lewis Dot Diagrams are used to just represent the valence electrons. • Hydrogen: • Helium: H He
How to Fill in Lewis Dot Diagrams • Start at the top and then fill in going clockwise. • Can only have up to a maximum of 8 dots around the atomic symbol. C N B
Charged Elements • Elements can become charged if the there is a change in the number of electrons • Elements try to get to the electron configuration of the closest noble gas –full valence shell. • Charged elements are known as ions. • Positively Charged Ion Cation • Negatively Charged Ion Anion • Boron has 3 electrons in its valence shell • Must lose 3 electrons to achieve a full valance shell • Acquires a charge of +3 • Ion is B3+ • How elements react depends on their valence electrons.
Positively Charged • Generally, metals tend to lose valence electrons relatively easily. • Elements that can easily lose an electron are known as electron donors. • To remove an electron from the Group 1 metals requires relatively little energy. • As you move down the group it becomes easier to remove the valence electron. • Metals are less reactive as you move across the period to the right.
Negatively Charged • Since non-metals have a greater number of valence electrons, they must gain electrons to fill their valence shell. • Elements that can easily gain an electron are known as electron acceptors. • The Halogens are very reactive elements. • As you move down the group the elements become less reactive. • Non-metals are less reactive as you move across the period to the left.