Presentation on theme: "What is a Chemical Bond? A chemical bond is a force holding two or more atoms together to form a molecule."— Presentation transcript:
What is a Chemical Bond? A chemical bond is a force holding two or more atoms together to form a molecule.
Why do atoms form chemical bonds? Atoms tend to form chemical bonds to satisfy the “octet rule” Atoms share or transfer their valence electrons to fill their outermost energy level; either 2 (for hydrogen) or 8 electrons.
There are three types of chemical bonds we will study Ionic bonds Covalent bonds Hydrogen bonds
Ionic Bonds: Give & Take Ionic bonds form when atoms transfer (lose or gain) electrons with other atoms. Atoms with 5, 6,or 7 valence electrons tend to gain electrons to fill their outer shells. Gaining electrons makes the atom a negative ion. Atoms with 1, 2 or 3 valence electrons tend to lose electrons. Losing electrons makes the atom a positive ion.
Examples of Ionic Bonds Ionic bonds form easily between the group 1 metals and the group 17 non-metals These new ionic compounds are known as metallic salts. Sodium Chloride is a good example of an Ionic Compound
Sodium Chloride is an Ionic Compound Sodium (Na) has 1 valence electron in its third energy orbital Chlorine (Cl) has 7 valence electrons in its third energy level They form an ionic compound when Sodium’s electron is transferred to Chlorine Now Sodium is a 1+ ion and Chlorine is a 1- ion. Their opposite charges keep them attracted to each other Overall, the compound is electrically neutral. Other examples of Ionic Compounds include rust, baking soda and limestone
Properties of Ionic Compounds Crystal Shaped Solids High Melting Points Electrical Conductivity
Covalent Bonds: Good at Sharing Covalent bonds are formed when 2 or more atoms SHARE their valence electrons Usually formed between two non-metals: oxygen, carbon and nitrogen like to form covalent bonds Atoms with exactly half ( 1 or 4 electrons) of their valence electrons like to form covalent bonds.
Drawing a covalent bond Draw a molecule of methane. Start with 1 carbon atom (in middle) Add the correct number of hydrogen atoms needed to form covalent bonds that satisfy the octet rule.
Properties of Covalently Bonded Molecules Low melting point Low melting point Poor Conductors of electricity Poor Conductors of electricity Typically form “organic” compounds like fats, proteins & carbohydrates Typically form “organic” compounds like fats, proteins & carbohydrates
Polar vs Non-polar Covalent Bonds: Oil & Water don’t mix Some atoms tend to pull harder on the shared electrons in a covalently bonded molecule. This creates a positive side and a negative side of the molecule. We call these kinds of molecules “polar”, because the electrons are shared unequally, creating a molecule with positively charged pole and a negatively charged pole Water is a good example of a polar molecule. Many molecules important to living things are polar and dissolve easily in water. + _ +
Hydrogen Bonds: “Opposites attract” Hydrogen bonds form between two nearby water molecules The negatively charged oxygen end of one water molecule is attracted to the positively charged hydrogen end of another. Hydrogen bonds cause many unique properties of water: it’s “stickiness” to itself, its ability to dissolve all other polar substances easily, its ability to remain a liquid at a wide range of temperatures.
Non-polar molecules Molecules which share their electrons equally are non-polar. Oils and fats are non- polar. Their molecules don’t have an overall “charge”. That’s why oil & water don’t mix. They’re not attracted to each other.
So: How does soap clean? Soap has a polar “head” and a non-polar “tail” The polar head is attracted to water & the non-polar tail is attracted to dirty oils Each oil molecule is surrounded by a ring of soap molecules When the water is washed away, it carries an oil molecule with it carries an oil molecule with it