VALENCE ELECTRONS & BONDING

VALENCE ELECTRONS & BONDING

Chapter 4 VALENCE ELECTRONS • Valence electrons: • found in the outermost shell of an atom • determines the atom’s chemical properties. • So how do we know the number of valence electrons an element has? • It based on their group on the periodic table.

1 ve 8 ve 3 ve 5 ve 7 ve 2 ve 4 ve 6 ve

VALENCE ELECTRONS • Lets find some valence electrons. • Si • Xe • K • Ba • I • O • Al • P

OXIDATION NUMBERS • charge an atom would have if it were in a compound composed of ions. • AKA: charge • change in oxidation number represents number of electrons gained or lost in a chemical reaction.

+1 +3 -1 -3 +2 +4 -2

OXIDATION NUMBERS • Lets find some oxidation numbers • In • F • Rb • Sn • Ca • N • O

Lewis Structures • AKA: electron-dot structures or electron-dot diagrams. • Uses the number of valence electrons. • indicated by dots placed around the element’s symbol. • diagrams that show the bonding between atoms of a molecule. • Always place the element with the largest number of valence electrons first, next largest … • They can form ionic & covalent bonds

Ionic Bonds • TRANSFER of electrons from one bonding atom to another

Ionic Bonds • BaO • FIRST WE SEE HOW MANY ELECTRONS THEY ARE FOR EACH ELEMENT. • Ba = 2 • O = 6 • DRAW LEWIS STRUCTURE FOR OXYGEN

Ionic Bonds o Ba

Ionic Bonds MgCl2

COVALENT BONDING • chemical bond resulting from SHARING of electrons between 2 bonding atoms.

COVALENT BONDING • H2O • FIRST WE SEE HOW MANY ELECTRONS THEY ARE FOR EACH ELEMENT. • H = 2 • OXYGEN = 6 • DRAW LEWIS STRUCTURE FOR OXYGEN

COVALENT BONDING H O H

BONDING REVIEW Directions: Each slide provides information in a question answer format. Click once to see the question and then again for the answer.

Bonds Between Atoms Polyatomic Ions Ionic Covalent Metallic Network Solids Molecular Substance Polar Coordinate Covalent Nonpolar What are we going to learn about???

See if you can define the following words before starting the lesson… • Anion- negative ion • Cation-positive ion • Octet Rule- rule that states that atoms tend to gain, lose, or share electrons so that each atom has full outermost energy level which is typically 8 electrons. • Polyatomic Ion- charged group of covalently bound atoms • Monatomic Ion- ion formed from a single atom • Molecule-neutral group of atoms united by covalent bonds • Alloy-homogeneous mixture of metals • Unshared Pair- pair of electrons that is not involved in bonding but instead is held exclusively by one atom.

Marriage Forming of a bond is like marriage The breaking of a bond relates to a divorce. • More stable • exothermic Divorce • Less stable • Endothermic

Ionic Bonds • What is an Ionic Bond? • - An Ionic Bond is a chemical bond resulting from the TRANSFER of electrons from one bonding atom to another • When is an ionic bond formed? - An ionic bond is formed when a cation (positive ion) transfers electrons to an anion (negative ion).

What are some characteristics of an ionic bond? • Crystalline at room temperatures • Have higher melting points and boiling points compared to covalent compounds • Conduct electrical current in molten or solution state but not in the solid state • Polar bonds

Covalent Bonds • What is an Covalent Bond? • - A covalent bond is a chemical bond resulting from SHARING of electrons between 2 bonding atoms. • What forms a covalent bond? - A covalent bond is formed between two nonmetals.

What are some characteristics of a covalent bond? • Covalent bonds have definite and predicable shapes. • Very strong • Low melting and boiling points

Covalent Bonds can have multiple bonds, so you should be familiar with the following… Single Covalent Bond- chemical bond resulting from sharing of an electron pair between two atoms. Double Covalent Bond- chemical bond resulting from sharing of two electron pairs between two atoms. Triple Covalent Bond-chemical bond resulting from sharing of three electron pairs between two atoms.

There are five different categories associated with covalent bonds. What are the 5 different categories? Covalent Network Solids Molecular Substance Polar Coordinate Covalent Nonpolar

First, we are going to look at Polar Covalent… c What is polar covalent? -Polar covalent is a description of a bond that has an uneven distribution of charge due to an unequal sharing of bonding electrons. The boy is not equally sharing with anyone else but rather taking all the food for himself.

Next, we are going to look at Non-Polar Covalent… What is non-polar covalent? -Non polar covalent is a covalent bond that has an even distribution of charge due to an equal sharing of bonding electrons. This couple is nonpolar because they are sharing the drink equally between them.

Next, we are going to look at Molecular Substances… What is a molecular substance? -A molecular substance is a substance that has atoms held together by covalent bonds. Name 2 Characteristics of a Molecular Substance. • Weak • Low melting and boiling points

Next, we are going to look at Coordinate Covalent… What is a Coordinate Covalent Bond? -A coordinate covalent bond is a bond formed when one atom donates both electrons that are shared. People donate their blood to help others just like atoms “donate” electrons to form stable octets. *Think about the party analogy!

Now, we are going to look at Network Solids… What is a Network Solid? Diphenylglycoluril assembles into a unique, two-dimensional hydrogen bonding network in the solid state, while exhibiting a twisted molecular structure. -A network solid is a solid that has covalently bonded atoms linked in one big network or one big macromolecule. Name 3 Characteristics of a Network Solid. • Poor conductors of heat and electricity • Hard / Strong • High melting and boiling points

Metallic Bonding Name 4 Characteristics of a Metallic Bond. What is a Metallic Bond? - A metallic bond occurs in metals. A metal consists of positive ions surrounded by a “sea” of mobile electrons. • Good conductors of heat and electricity • Great strength • Malleable and Ductile • Luster This shows what a metallic bond might look like.

Polyatomic Bonds Polyatomic ions usually have a charge because the collection of atoms has either gained an extra electron or else it has lost an electron. What is a Polyatomic Bond? - A polyatomic bond is charged group of covalently bonded atoms. It is made up of more than one atom.

Notice all the different types of shapes that the atoms can take on because of their bonding… Linear Trigonal Planer Trigonal Bipyramidal Tetrahedral Octahedral

Just as a summary to what each bond looks like…

REVIEW Now that you have completed the review provided you may wish to practice for your test by answering the following regents questions. The question is presented in the same way that http://regentsprep.org/ does them. If you would like to get reasons to why your answers were incorrect you can find the explanations there. After you have gotten your answer, click the mouse and the right answer will show up.

If you chose…

Chemical Bonds

Atom – the smallest unit of matter “indivisible” Helium atom

electron shells • Atomic number = number of Electrons • Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells. • Electron shells determine how an atom behaves when it encounters other atoms

Electrons are placed in shells according to rules: • The 1st shell can hold up to two electrons, and each shell thereafter can hold up to 8 electrons.

Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons Gain 4 electrons • C would like to • N would like to • O would like to Gain 3 electrons Gain 2 electrons

Why are electrons important? • Elements have different electron configurations • different electron configurations mean different levels of bonding

VALENCE ELECTRONS & BONDING