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The Atom

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.

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The Atom

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  1. 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.

  2. 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.

  3. Representing Elements • To represent elements we use the symbol A X Z • X – Atomic symbol • Z – Atomic number (p+) • A – Mass number (p+ + n0)

  4. Example • Na  Sodium • Atomic Number = 11  11 protons • Mass Number = 23  23 - 11 = 12 neutrons • Neutral  # electrons = # protons = 11 23 Na 11

  5. 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

  6. 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.

  7. Properties of the Types of Elements

  8. 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.

  9. Examples of Electron Configurations

  10. 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?

  11. Valence Electrons

  12. 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.

  13. 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

  14. 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)

  15. 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.

  16. Isotope Example (Hydrogen) 0 neutrons 1 neutron 2 neutrons • 2H and 3H are known as deuterium and tritium. • Also called “heavy” hydrogen

  17. Lewis Dot Diagrams • Lewis Dot Diagrams are used to just represent the valence electrons. • Hydrogen: • Helium: H He

  18. 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

  19. 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.

  20. 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.

  21. 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.

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