Chapter 5 – Atoms & Bonding

Electron Shells Electrons aren’t the same distance from the nucleus. They are arranged in shells or energy levels. The period # tells you the number of energy shells for each element in a period Each shell can hold only a certain number of electrons. Electrons are in constant motion and can move between levels. Electrons closest to the nucleus have the least energy and the electrons in the outermost shell have the most energy The orbitals are not set paths like planets around the sun. They are more like boundaries to predict where you will find electrons most of the time based on energy. This is just a model to help visualize the energy levels.

Shells First shell = 2 electrons “the sports car” Second shell = 8 electrons “the mini van” Third shell= 8 electrons “another mini van”

Lets practice! According to the periodic table how many energy shells would be in an atom of: Sodium (Na) Oxygen (O) How do you know?

Valence Electrons & Bonding The electrons in the outer shell are called valence electrons The number of valence e- in an atom of an element determines how the atom can bond with other atoms The family # tells you the number of valence electrons for each element in the family (A groups only)

Lets practice! According to the periodic table how many valence electrons do the following atoms have: Sodium (Na) Oxygen (O) How do you know?

Valence Electrons & Bonding Atoms are more stable (less likely to react) when they have 8 valence electrons Atoms can gain or lose electrons in order to have 8 valence electrons Chemical Bond – the force of attraction that holds two atoms together The valence e- are the ones involved in bonding. The further away from the nucleus the less the force of attraction between the positive nucleus and negative e-. This is why the valence e- are easily gained or lost to form new chemical bonds

Valence Electrons & Bonding Electron Dot Diagram – includes the symbol for the element surrounded by dots…the dots show the valence electrons

Chapter 5 – Atoms & Bonding Section 3 - Covalent Bonds Standards 3.b – Students know that compounds are formed by combining two or more different elements and that compounds have properties that are different from their constituent elements. 7.c – Students know substances can be classified by their properties, including their melting temperature, density, hardness and thermal and electrical conductivity

Electron Sharing Covalent Bond – a chemical bond formed when two atoms share electrons

How many Bonds? Use electron dot diagrams to set up an atom to have 8 valence electrons Electrons can be shared in order to fulfill the octet rule (8 valence electrons)

How many Bonds? Double Bond – two pairs of electrons being shared between two atoms Triple Bond – three pairs of electrons being shared between two atoms

Chapter 5 – Atoms & Bonding Section 2 – Ionic Bonds Standards 3.b – Students know that compounds are formed by combining two or more different elements and that compounds have properties that are different from their constituent elements. 3.c – Students know that atoms and molecules form solids by building up repeating patterns, such as the crystal structure of NaCl or long-chain polymers

Ions Ion – an atom or group of atoms that has become electrically charged When an atom loses an electron it has a positive charge When an atom gains an electron it has a negative charge Element Ion Hydrogen   H + Potassium   K + Sodium   Na + Barium   Ba 2+  Calcium   Ca 2+  Magnesium   Mg 2+ Aluminum   Al 3+   Boron B 3+ Lithium   Li +   Element Ion Flouride   F -  Chloride   Cl - Bromide   Br -   Iodide   I -   Oxide   O 2-   Sulfide   S 2-   Nitride   N 3-   Phosphide   P 3-   10 electrons 8 valence e-

Ions Ionic Bond – the attraction between two oppositely charged ions Ionic bonds form as a result of the attraction between positive and negative ions Ionic Compound – compound that consists of positive and negative ions

Chemical Formula & Names Chemical Formula – combination of symbols that shows the ratio of elements in a compound Ex. MgCl2 or NaCl or K2S When ionic compounds form, the ions come together in a way that balances out the charges on the ions Subscript – tells you the ratio of elements in the compound Ex. MgCl2 - 1 Magnesium ion and 2 Chlorine ions

Naming Ionic Compounds The name of the positive ion goes first Then the name of the negative ion If the negative ion is an element, add the ending –ide If the negative ion is polyatomic, leave the name the same Mg2+ + O2-  MgO Magnesium Oxide Na+ + CO32-  Na2CO3 Sodium Carbonate

Properties of Ionic Compounds The characteristic properties of ionic compounds are: Crystal Shape – orderly 3-D shape High Melting Point – ionic bonds are strong Electrical Conductivity – when dissolved in water, ionic compounds conduct electricity

Practice with Ionic Bonds Examples: Na + Cl  NaCl Na+ + Cl–  NaCl Mg + Cl  MgCl Mg2+ + Cl–  MgCl2 Ca + O  CaO Ca2+ + O2–  CaO Al + O  AlO Al3+ + O2–  Al2O3