8 th Grade Science

Atomic Structure Atoms have a nucleus that contains Protons and Neutrons Electrons are contained in shells that surround the nucleus An atom is made of mostly empty space Protons have a positive charge Electrons have a negative charge Neutrons are Neutral

Valence Electrons Each electron shell can hold a certain number of electrons Electron shells are filled from the inside out Noble Gases have full outer electron shells All other elements have partially filled outer electron shells Electron ShellNumber of Electrons

Valence Electrons The electrons in the outer most electron shell are called valence electrons The shell containing electrons that is furthest from the nucleus is called the valence shell The number of electron shells with electrons is the same as the period number

Noble Gas Stability Noble gases are usually unreactive This is because they have full valence shells An element with a full valence shell is a happy element For two atoms to join together atoms must gain, lose or share electrons Elements with full valence shells do not easily gain or lose electrons

Noble Gas Stability Atoms want to gain stability Atoms will try to gain or lose electrons to have a full valence shell Metals try to lose electrons Non-Metals try to gain electrons

Becoming An Ion Electrons are negatively charged Protons are positively charged Neutral atoms do not have a charge because the number of protons is the same as the number of electrons When atoms gain or lose electrons they become positively or negatively charged An atom with a charge is called an Ion

In covalent bonding, atoms still want to achieve a noble gas configuration (the octet rule). But rather than losing or gaining electrons, atoms now share an electron pair.

Covalent & Ionic Bonds

LET’S FIRST REVIEW IONIC BONDING

In an IONIC bond, electrons are lost or gained, resulting in the formation of IONS in ionic compounds. FK

FK

FK

FK

FK

FK + _

FK + _ The compound potassium fluoride consists of potassium (K + ) ions and fluoride (F - ) ions

FK + _ The ionic bond is the attraction between the positive K + ion and the negative F - ion

Covalent Bonds

So what are covalent bonds?

In covalent bonding, atoms still want to achieve a noble gas configuration (the octet rule).

In covalent bonding, atoms still want to achieve a noble gas configuration (the octet rule). But rather than losing or gaining electrons, atoms now share an electron pair.

In covalent bonding, atoms still want to achieve a noble gas configuration (the octet rule). But rather than losing or gaining electrons, atoms now share an electron pair. The shared electron pair is called a bonding pair

Cl 2 Chlorine forms a covalent bond with itself

Cl How will two chlorine atoms react?

Cl Each chlorine atom wants to gain one electron to achieve an octet

Cl Neither atom will give up an electron – chlorine is highly electronegative. What’s the solution – what can they do to achieve an octet?

Cl

octet

Cl circle the electrons for each atom that completes their octets octet

Cl circle the electrons for each atom that completes their octets The octet is achieved by each atom sharing the electron pair in the middle

Cl circle the electrons for each atom that completes their octets The octet is achieved by each atom sharing the electron pair in the middle

Cl circle the electrons for each atom that completes their octets This is the bonding pair

Cl circle the electrons for each atom that completes their octets It is a single bonding pair

Cl circle the electrons for each atom that completes their octets It is called a SINGLE BOND

Cl circle the electrons for each atom that completes their octets Single bonds are abbreviated with a dash

Cl circle the electrons for each atom that completes their octets This is the chlorine molecule, Cl 2

O2O2 Oxygen is also one of the diatomic molecules

How will two oxygen atoms bond? OO

OO Each atom has two unpaired electrons

OO

OO

OO

OO

OO

OO

Oxygen atoms are highly electronegative. So both atoms want to gain two electrons. OO

Oxygen atoms are highly electronegative. So both atoms want to gain two electrons. OO

OO

OO

OO

OO

O O Both electron pairs are shared.

6 valence electrons plus 2 shared electrons = full octet O O

6 valence electrons plus 2 shared electrons = full octet O O

two bonding pairs, O O making a double bond

O O = For convenience, the double bond can be shown as two dashes. O O

O O = This is the oxygen molecule, O 2 this is so cool! !

Answer these questions: An atom that gains one or more electrons will have a ____________________ charge. An atom that loses one or more electrons will have a ____________________ charge. An atom that gains or loses one or more electrons is called an ____________. A positive ion is called a ______________ and a negative ion is called an _______________. POSITIVE NEGATIVE ION CATION ANION “An-Eye-On” “Cat-Eye-On”

What is an ionic bond? Atoms will transfer one or more ________________ to another to form the bond. Each atom is left with a ________________ outer shell. An ionic bond forms between a ___________ ion with a positive charge and a ________________ ion with a negative charge. Example B1: Sodium + ChlorineExample B2: Magnesium + Iodine ELECTRONS COMPLETE METAL NONMETAL

What is a covalent bond? Atoms ___________ one or more electrons with each other to form the bond. Each atom is left with a ________________ outer shell. A covalent bond forms between two _________________. Example C1: Hydrogen + HydrogenExample C2: 2 Hydrogen + Oxygen SHARE COMPLETE NONMETAL