Notes 6 - Ions & Chemical Bonding

Unstable Atoms ► In order to be stable, an atom needs a certain number of valence electrons  2 valence e - if it only has 1 energy level  8 valence e - if it has 2+ energy levels ► Most atoms are unstable ► In order to become stable, atoms may:  take electrons from other atoms  lose electrons to other atoms  share electrons

► To determine if an atom is stable or unstable, you must look at the number of valence electrons. Neon Example: Neon has 8 electrons in the last level, so it is stable

Carbon Hydrogen ► Carbon has 4 electrons in the last level, so it is unstable ► Hydrogen has 1 electron in the last level, so it is unstable as well

The Noble Gases ► Group 8 elements all have 8 valence electrons ► They are naturally stable ► They do not give, take, or share electrons ► They don’t react or form bonds with other atoms

Ion Formation ► Ion – an atom that gains or loses one or more electrons ► Ions form so that atoms can become stable ► Atoms with a valence of 3 or less will lose electrons ► Atoms with a valence of 5 to 7 will take electrons ► When atoms lose or take electrons, they become charged

Why do ions have a charge? ► Atoms that have lost or gained electrons have unequal numbers of protons and electrons ► Atoms that gain electrons have more electrons (e-) than protons (p+), so they become negative ions ► Atoms that lose electrons have more protons (p+) than electrons (e-), so they become positive ions

Examples of Ions Na + Li + Ca 2+ Fe 2+ Al 3+ Cl - F - O 2- S 2- N 3-

Metals vs Non-metals ► Metals are unstable ► Metals have valences of 1, 2, or 3 ► Metals give up valence electrons and become positive ions ► EX. Lithium  Valence of 1  Loses 1 electron  Becomes a positive ion (Li + )

Metals vs Non-metals ► What is a magnesium atom’s valence?  2 (It is in Group 2 – that is how you know) ► So how many electrons would it give up to become stable? 2222 ► What is a sodium atom’s valence? 1111 ► So how many would it give up? 1111

Metals vs Non-metals ► Non-metals are unstable except for the noble gases ► Non-metals have valences of 4, 5, 6, or 7 ► Non-metals take valence electrons and become negative ions ► EX. Chlorine  Valence of 7  Gains 1 electron  Becomes a negative ion (Cl - )

Metals vs Non-metals ► What is an oxygen atom’s valence? 6666 ► How many electrons would it need to take to become stable? 2222 ► What is a fluorine atom’s valence? 7777 ► How many would it need to take? 1111

Chemical Bonding ► Chemical bonding – when 2 or more unstable atoms stick together in order to become stable ► Chemical bond – an attractive force that holds atoms together ► Atoms may bond together by:  opposite ions attracting (positive  negative)  sharing electrons

Chemical Bonding ► There are 3 types of chemical bonds: 1.Ionic bonds 2.Covalent bonds 3.Metallic bonds

Ionic Bonds – What are they? ► Ionic bond – a bond formed by the attraction between positive and negative ions ► Ionic bonds form between metal atoms and non-metal atoms  Metal atom forms the positive ion (gives e - )  Non-metal atom forms the negative ion (takes e - )

Ionic Bonds – How do they form? ► A non-metal atom with more than 4 valence electrons takes electrons from a metal atom ► The non-metal atom becomes a negative ion ► The metal atom becomes a positive ion ► The opposite ions attract forming an ionic bond ► Ionic compounds are generally solids with high melting points (Ex. NaCl – Salt)

More Atom Humor

Covalent Bonds – What are they? ► Covalent bond – A bond formed when atoms share one or more pairs of valence electrons in order to become stable  EX. H 2 O ► Atoms that share more than one pair of electrons may form double or triple bonds  EX. O 2 ► Covalent bonds form between atoms of non-metals

► Metallic Bonds – bond formed between metal atoms ► Electrons can move between atoms ► Form between atoms of the same element ► 2 different metals can’t bond to each other  Ex. Iron atoms can bond to iron atoms metallically, but copper atoms can’t bond to iron atoms Metallic Bonds – What are they?

Remember… ► Unstable atoms form bonds to become stable ► Unstable atoms give, take, or share electrons ► The Octet Rule – “I’ve got 8, so I’m straight”  Atoms with 8 valence electrons are stable