Physical Science Chapter Six 1

Chemical Bonds The force that holds atoms or ions together. http://www.youtube.com/watch?v=QqjcCvzWwww 2

Ionic Bonding Reactivity of an atom depends on its electron configuration. Atoms will be stable if their outermost energy levels are full. Some atoms will achieve stability by transferring electrons. 3

Electron Dot Diagram Unlike Bohr’s model of an atom, the electron dot diagram uses dots to represent valence electrons. For example, Potassium (K) is located in group 1A. Group 1A elements all have only one valence electron. When drawing the electron dot diagram for potassium, you only have to draw one electron dot. 4

Ionic Bonding When an ionic bond occurs, the number of protons no longer equals the number of electrons. When one atom gives up an electron, it has more positively charged protons than electrons. The atom then becomes a positively charged ion called a cation. 6

Ionic Bonding When an atom gains an electron, it contains more electrons that protons. The atom becomes a negatively charged ion called an anion. Anions are named by their element with a suffix. Cations are named by their elements. 7

Ionic compounds Compounds that contain ionic bonds are called ionic compounds. Chemical formulas are used to show the ratio of the atoms or ions of elements in the compounds. 8

Ionization Energy The amount of energy needed to remove an electron from an atom is called ionization energy Ionization energy usually increases from left to right across a periodic table which means that nonmetals would be more likely to gain electrons and metals would be more likely to lose electrons. 9

Naming Binary Ionic Compounds Binary compounds are made from only two elements. To name a binary ionic compound, list the cation followed by the anion. The cation is named after the element. The anion is named after its element followed by the suffix ide. 10

Metals with multiple ions Some transition metals can form more than one type of ion. For example, you can have a copper (I) ion with a 1+ charge or a copper (II) ion with a 2+ charge. To name the different ions of the same element, you write the name of the element followed by the roman numeral in parentheses. 11

Polyatomic Ions A covalently bonded group of atoms that has a positive or negative charge and acts as a unit is called a polyatomic ion. Hydroxide and ammonium are examples of polyatomic ions. 12

Writing formulas for Ionic Compounds The charges in an ionic compound must cancel each other. If an atom of sulfur that gains two electrons reacts with an atom of sodium that loses one electron, there must be two atoms of Na for every one atom of S. 13

Covalent Bonds A covalent bond is a chemical bond in which two atoms share a pair of valence electrons. Covalent bonds can be represented in many ways. It is often represented by its structural formula. 14

Molecules A neutral group of atoms joined by a covalent bond form a molecule. Two atoms of Hydrogen covalently bonded together form a molecule. Many nonmetal elements exist as diatomic molecules- meaning that they consist of two atoms. 15

Polar Covalent Bonds Molecules of an element share equal attraction of electrons Molecules of a compound may not be shared equally. When electrons are not shared equally, a polar covalent bond occurs. 16

Covalent Bonds- Structural Formula An example of the structural formula of a covalent bond would be if you had two hydrogen atoms covalently bonded together. It would be represented by H-H. Each atom of hydrogen provides only one valence electron, but if the two atoms share electrons, they have a complete energy level. 17

Covalent bonds- structural formula Sometimes atoms have to share more than one electron to be complete. Nitrogen has 5 valence electrons. So two nitrogen atoms would have to share three electrons so that both atoms could have 8 valence electrons. 18

Describing Molecular Compounds The name and formula of a molecular compound describe the type and number of atoms in a molecule of the compound. In naming the compound, the most metallic element appears first. If both the elements are in the same group, the more metallic element is closer to the bottom of the group. 19

Describing Molecular Compounds Use ide as the suffix. The prefix usually indicates the amount of atoms of each element. Example CO2 is carbon dioxide. There are two atoms of oxygen, and di- stands for two. 20

Metallic Bonds The attraction between a metal cation and the shared electrons that surround it is called a metallic bond. The electrons of metals are mobile. This helps to explain that metals are good conductors and very malleable. Metallic bonds are strong and more flexible allowing for their malleability. 21

Alloys Alloys are mixtures of two or more elements, at least one of which is a metal. Alloys have characteristic properties of metals. When you combine metal together with other elements, you can form stronger more desirable substances. Bronze, brass, and steel are common examples of alloys.