Chemistry 10 Ions (Cations & Anions) Bohr Diagrams Lewis Dot Diagrams Old Textbook, pages 138-147 for more review and reading.

Review Atoms are the basic building units of matter around us. An atom consists of three basic particles: positively charged protons, negatively charged electrons and neutral neurons. Electrons revolve around the nucleus. The nucleus is at the center of the atom and consists of protons and neutrons. The pathway of electrons around the nucleus is called orbit. An atom is neutral due to equal number of electrons in the orbits and number of protons in the nucleus. All ions want to obtain an electron arrangement like that of the Nobel gases, a full valence shell.

Words To Know Ion – An atom, or group of atoms, that has a net positive or negative charge. Cation – An ion with a net positive charge, due to the loss of one or more electrons from a neutral atom. Usually formed by metals. Example: Sodium atom, Na, can readily lose an electron to become a sodium cation, Na+ Anion – An ion whose net charge is negative due to an increase in the number of electrons. Usually formed by non-metals. Example: Chlorine atom, Cl, can gain an electron to become a chloride ion, Cl- Monatomic Ion – Contains only one atom, such as Fe3+, Mg2+ Polyatomic/Molecular Ion - Two or more atoms can combine to form an ion that has a net positive or negative charge, such as OH-, NH4+

Examples A sodium atom, Na, whose atomic number is 11, has 1 electron in its valence shell, surrounding inner shells with 2 and 8 electrons. A sodium atom loses its extra becoming a cation. Na –> Na+ + e- A chlorine atom, Cl, whose atomic number is 17, has 7 electrons in its valence shell. Thus a chlorine atom gains an electron to attain a stable configuration with 8 electrons in valence shell. Chlorine forms an anion in this process. Cl + e- –> Cl- Valence Shell: The outer shell of the atom. Electrons form a 2, 8, 18 & 32 arrangement around shells; the electrons that occupy the valence shell are called valence electrons

Bohr Diagrams A Bohr diagram is a simplified visual representation of an atom that was developed by Danish physicist Niels Bohr in 1913. The diagram depicts the atom as a positively charged nucleus surrounded by electrons that travel in circular orbits about the nucleus in discrete energy levels.

Rules For Drawing Bohr Diagrams Consult the Periodic Table of the Elements for the type of atom you are going to represent in a Bohr diagram. Write down its atomic number and mass number. The atomic number is the number of protons, and the mass number is the number of protons and neutrons. The number of electrons is equal to the number of protons. See which row of the Periodic Table your element is in. Elements in the first row (hydrogen and helium) have one energy level, those in the second row will have two energy levels and so on.

 Draw a circle to represent the nucleus of the atom. Write the symbol for the element, the number of protons and the number of neutrons inside this circle. Draw one or more circles around the nucleus depending on which row of the Periodic Table your element comes from. Each ring represents a different energy level for the electrons.

Rules For Drawing Bohr Diagrams Draw electrons as dots on the rings that represent the energy levels. Each ring has a maximum number of electrons that it can hold. The first (inner) ring can only hold 2 electrons, the second level can hold 8, the third can hold 18 and the fourth holds 32.

Bohr Diagram Which ion is this?

Electron Dot Diagrams American chemist Gilbert Lewis invented electron dot diagrams to help him understand and predict the bonding that occurs between atoms. Also called Lewis diagrams, they represent the atom of an element by showing only the outer valence electrons and the chemical symbol.

Electron Dot Diagrams Electron Dot Diagrams Electron dots representing electrons are usually placed around the element symbol at the points of a compass (North, South, East & West). Electron dots are placed singly first until the 5th electron is reached; at this point the electrons are then paired. Pairs of electrons in Electron Dot Diagrams are called Lone Pairs. Single electrons in Electron Dot Diagrams are called Bonding Electrons, because they are looking for another electron to make a pair (bond) with.

Bonding Ionic Covalent

Ionic Bonding Opposite ions attract each other to form an ionic bond. Anions and cations will form ionic compounds – the attraction between the positive and negative ions will form ionic bonds. By using Electron Dot and Bohr Diagrams, we can see how ionic bonds are formed.

Covalent Bonding Atoms that share a pair of electrons are joined by a covalent bond. A neutral particle that is composed of atoms joined together by covalent bonds is called a molecule; substances that are composed of molecules are called molecular compounds.

Steps for drawing covalent bonds 1- Write the symbols for each element. 2 - Use different colored circles to create the Lewis structure for each. 3 - Rearrange the electrons (or circles) to pair up electrons from each atom. 4 - Draw circles to show the sharing of electrons. 5 - Draw the bond structure using symbols and lines. Use one line for each pair of electrons that is shared. 6 - Write the chemical formula for each molecule.