Chapter 5: The Structure of Matter Section 1: Ionic Bonds

The Structure of Matter Bonding of atoms When two or more atoms join, a bond forms. Bonded atoms are the source of all substances. The kinds of elements in the bond determines the properties of the substance formed. Compounds are made from bonded atoms.

Ionic Bonds When a metal element bonds with a nonmetal element, an ionic bond is formed. Definition: ionic bond – a bond between oppositely charged ions. Example: Sodium has only 1 valence electron. Sodium wants to LOSE this electron! Chlorine has 7 valence electrons. Chlorine wants to GAIN an electron! SO….

The Structure of Matter You need this example in your notes. . . . . . . Na Cl . . Has one extra… Needs one more…

The Structure of Matter You need this example in your notes. The two atoms will BOND. . . . . 1+ . . 1- Na Cl . . Now Sodium’s 2nd Energy Level has 8… And Chlorine’s 3rd Energy Level has 8.

Electron Transfer! When these two elements bond, Chlorine steals the electron from sodium. Now Sodium has a positive charge and has 8 valence electrons. It is now “happy”. Chlorine now has a neg. charge. It has 8 valence electrons, and is “happy”. The + and – ions attract each other and form the compound “sodium chloride”.

Ionic Compound Properties Ionic compounds are usually brittle, and crumble easily. They also have high melting temperatures..

Ionic Compound Properties Ionic compounds can conduct electricity in water. When dissolved in water, the ions come apart. This allows electricity to flow through them. - - + + - + - + - + -

Writing Ionic Compound Formulas Now that we know how and why ionic bonds form, we can write chemical formulas. Definition: chemical formula – a method of showing the elements that make up a compound. Example: Na1Cl1 tells us that: Salt is made up of 1 Sodium atom and 1 Chlorine atom. What about MgF2 ? It is made up of ____ Magnesium atoms and ____ Fluorine atoms.

Ionic Compound Formulas Lets take a closeer look at those compounds. Na has a charge of 1+, right? Cl has a charge of 1_, right? The charges cancel out! When an ionic compound forms, it must have the same number of + and _ charges to be neutral.

Lets look at how Magnesium and Fluorine bond... Ionic Compound Formulas Lets look at how Magnesium and Fluorine bond... Magnesium Ion Fluorine Ion MG2+ F1- To make a compound with them, you have to make sure the charges cancel. MG2+ F1- It takes 1 Magnesium (Mg1) It takes 2 Fluorine (F2) MgF2 F1-

Chapter 5: The Structure of Matter Sugar is a covalent compound. Section 2: Covalent Bonds

Covalent Bonds When a bond forms between two nonmetal elements, it is called a Covalent Bond. Water and sugar are two examples of covalent compounds. Salt is an ionic compound. Salt does NOT have molecules. A covalent bond is formed when atoms share one or more PAIRS of electrons. Covalent bonds are formed in order to fill the outer energy level.

Properties of covalent compounds. Most covalent compounds have relatively low melting temperatures. Covalent compounds do not conduct electricity when melted or dissolved. Molecules are not made up of ions, so they have no charge. Since molecules have no charge, electricity cannot flow through them. Sugar melts easily to become caramel!

This is the dot diagram for the O2 Molecule. Covalent Bonds Some nonmetal elements can form covalent bonds with themselves For example: Oxygen can bond with other oxygen atoms by forming covalent bonds. The atoms will share bonds with each other in order to become happy. . . . . This is the dot diagram for the O2 Molecule. . . _ . . . _ . . . O O Each line represents 2 SHARED electrons.

Covalent bonds make molecules. The simplest molecule is H2. When a molecule is made up of only 2 atoms, it is called “diatomic”. There are 7 elements that make diatomic molecules with themselves naturally.

The Diatomic Elements The 7 Diatomic Elements are: Hydrogen – H2 Nitrogen – N2 Oxygen – O2 Fluorine – F2 Chlorine – Cl2 Bromine – Br2 Iodine – I2

Naming Covalent Compounds In order to name a covalent compound, you add a prefix to the element names. The prefix you add depends on how many atoms are in the compound. The element with the most atoms comes 2nd. If the 1st element only has 1 atom, it doesn’t get a prefix.

Here are the prefixes for naming covalent compounds: 1 – Mono 2 – Di 3 – Tri 4 – Tetra 5 – Penta 6 – Hexa 7 – Hepta 8 – Octa 9 – Nona 10 - Deca

The Compound CO2 has: 1 Carbon atom. 2 Oxygen atoms Example… It does NOT get a prefix. Too bad, Carbon.  2 Oxygen atoms It gets the prefix “Di” Our compound is called… Carbon Di-Oxide!

The Compound N2O5 has: Example… 2 Nitrogen atoms. 5 Oxygen atoms It gets the prefix “Di” 5 Oxygen atoms It gets the prefix “Penta” Our compound is called… Di-Nitrogen Pent-Oxide (the a was dropped)

Sometimes, compounds are not just ionic or covalent…they can have both kinds of bonds. Definition: polyatomic ions – groups of covalently bonded atoms joined by ionic bonds. Polyatomic ions are written in parentheses. For example: Hydroxide is (OH). Cyanide is (CN) Carbonate is CO3 The compound Sodium Hydroxide would be written as Na(OH)

Ionic Compound Formulas That’s all, folks.