Chapter 5.3 Covalent Bonds Standards: 8.3.b. Students know that compounds are formed by combining two or more elements and that compounds have properties that are different from their constituent elements. 8.7.c. Students know substances can be classified by their properties including their melting temperature, density, hardness, and thermal and electrical conductivity. How Covalent Bonds form Covalent bond: formed when two atoms SHARE electrons Formed between a 2 nonmetals Molecule: neutral group of atoms joined by covalent bonds How many bonds? Draw the electron dot diagrams of Fluorine. Do this again. HINT: How many valence electrons does fluorine have? Now draw the electron dot diagrams of 2 oxygen atoms right next to each other. HINT: How many valence electrons does oxygen have? How many bonds? Now draw the electron dot structure of 2 Nitrogen atoms. HINT: How many valence electrons does each have? Single, Double, & Triple Bonds A single bond has 2 electrons shared. 1 pair shared electrons A double bond has 4 electrons shared. 2 pair shared electrons A triple bond has 6 electrons shared. 3 pairs shared electrons Molecular compounds Compared to ionic bonds, molecular compounds generally have lower melting points and boiling points. Unlike ionic compounds, molecular compounds do not conduct electric current when melted or dissolved in water. Boiling point It takes more energy to boil ions than molecules. Ionic bonds are stronger so you need more energy to break them up. Conductivity Ions have charged particles, so they conduct electricity. Molecules do NOT have charge particles, so they DO NOT conduct electricity. Unequal Sharing of Electrons Electron sharing is like playing tug of war. Not all electrons are shared equally. Unequal sharing of electrons causes the bonded atoms to have slight electrical charges. Polar vs Nonpolar A covalent bond where electrons are shared unequally is known as POLAR. Polar because it has poles, like the north an south pole. A covalent bond where electrons are shared equally is called NONPOLAR. Real life example: Water is polar. What does polar mean? Oil is nonpolar. What does nonpolar mean?