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Chemical Bonding is the joining of atoms to form molecules and compounds Atoms bond to achieve a state of stability (stable outer shell of electrons) It is the transfer or sharing of electrons Bonding occurs during a chemical reaction and results in a chemical change (example: Na + and Cl - ions react to give a molecule, NaCl)

Question 1 What are atoms trying to achieve? A – a full inner shell B – a stable state C – 6 outer electrons D – Halogen gas structures

Question 2 When does bonding occur? A - During a physical change B – When a current flows in a metal C – During a chemical reaction D – As a result of heating

Question 3 What do electrons do during bonding? A- They double in mass B - They go to new levels C - They share or transfer D - They move to lower energy levels

A measure of the attraction an atom has for bonding electrons Fluorine is the most reactive non-metal, and therefore has the greatest attraction for the electron – it is the most electronegative element On the periodic table, the general trend is that electronegativity increases going up a group and right across a period The difference in electronegativites can help predict what type of bond will be formed

Question 4 Which is the most electronegative atom? A – Chlorine B – Argon C - Francium D - Fluorine

Question 5 Electronegativity shows which trend? A- Decreases going down a period B – Increases going across a period C – Increases going down a group D – Decreases going across a group

Question 6 Electronegativity means: A – how easy it conducts B – how many electrons it has C – the type of anion it forms D – the attraction for bonding electrons

MetalsNonmetals Conduct heat and electricity Typically shiny Can be hammered into sheets or drawn into wire Lose electrons to form cations 80% of elements are metals Bad conductor of heat and electricity Brittle, waxy, or gaseous Cannot be hammered into sheets or drawn into wire Gain electrons to form anions 20% of elements

Question 7 What is NOT a property of Non - metals? A- Bad conductor of heat and electricity B- Brittle, waxy, or gaseous C- Cannot be hammered into sheets or drawn into wire D- Typically shiny

Question 8 What is NOT a property of metals? A- Conduct heat and electricity B- Can be hammered into sheets or drawn into wire C- Brittle D- Lose electrons to form cations

Question 9 A new element conducts electricity, is shiny and can be bent into shape. Is it? A – Metalloid B- Metal C- Non metal D – A halogen

Ionic Covalent Metallic

Question 10 Which is not a type of bond? A- Metallic B- Covalent C- Allotropic D- Ionic

Occurs between a metal and a nonmetal Occurs between two atoms with a large difference in electronegativity (typically 1.7 or greater) Electrons are completely transferred, forming atoms with net positive and net negative charge Salts are often formed Continued

tend to have high melting and boiling points can't melt them with a Bunsen burner very hard and very brittle conduct electricity when they dissolve in water Continued

Question 11 What type of elements are involved in ionic bonding? A- 2 metals B- A metal and a non metal C- 2 non metals D- A noble gas and a metal

Sodium and Chlorine The sodium atom has one valence electron and a very low electronegativity, so it will lose an electron and become an ion with a charge of +1. The chlorine atom has a very high electronegativity, so it will attract an electron and become and ion with a charge of -1 The reaction is thus: Na + + Cl - NaCl (table salt)

Question 12 In sodium chloride what has happened to the electrons? A- One electron has shared B- One electron has transferred to Cl + C- One electron has transferred to Na + D- One electron has transferred to Cl -

Occurs between atoms with similar or identical electronegativities (difference less than 1.7) Atoms “gain” electrons to obtain a stable configuration Occurs between two nonmetals Common examples are diatomic molecules (Cl 2, F 2, N 2, etc.)

generally have much lower melting and boiling points are soft and squishy (compared to ionic compounds) tend to be more flammable than ionic compounds don't conduct electricity in water aren't usually very soluble in water

Question 13 Covalent bonding occurs between? A- 2 metals B- A metal and a non metal C- 2 non metals D- A noble gas and a metal

Question 14 What happens to the electrons in a covalent bond? A- They are transferred B- They are shared C- They become delocalized D- They form a sea of electrons

Chlorine Molecule (Cl 2 ) Each chlorine atom has seven valence electrons, so by sharing one, the atoms can obtain stable electron configurations.

Question 15 Chlorine is in group 17. How many electrons does it need to share to have a stable octet? A – 0 B- 1 C- 2 D- 3

Occurs between atoms with low electronegativity Occurs between atoms with 1, 2, or 3 valence electrons (many vacancies in shell) Electron clouds overlap, allowing electrons to become delocalised (move freely inside the structure) Positively charged nuclei and negatively charged electrons hold the metal together with strong forces of attraction

Question 16 Why are metals good conductors? A- They have high melting point B – They have delocalized electrons C – They have low densities D – They are malleable

Question 17 Which of the following is covalently bonded? A - NaCl B – CO C – KBr D – An alloy of copper and zinc (brass)

Question 18 Which compound will transfer electrons? A – NH 3 B – H 2 O C – CH 4 D - CaO

REMEMBER!! Electronegativity – the relative ability of an atom in a molecule to attract shared electrons to itself

Polarity when a molecule acts like a little magnet one side of the molecule has more electrons than the other side

Polarity Only covalent bonds can be polar A polar covalent bond results when electrons are shared unequally by nuclei One atom attracts the electrons more than the other atom

Polarity The polarity of a bond depends on the difference of electronegativity. This difference also helps to predict which type of bond will form. The larger the difference the more ionic the bond will be.

Dipole Moment A dipole moment results when a polar molecule has a center for positive charge separate from a center for negative charge The arrow starts on the positive side and points to the negative side. All polar bonds have a dipole moment.

Dipole Moment Ex. Water

Dipole Moment The polarity of water affects its properties Permits ionic compounds to dissolve in it Causes water to remain liquid at higher temperature

Can we rank the polarity? BondElectronegativityDifference in values Bond TypeRanking H - H(2.1)(2.1)2.1 – 2.1 = 0COVALENT S – H F – H Cl - H O – O O - H

Ions and Compounds

Lets take a look at this chart.

Ions and Compounds Why do the formation of an ion cause the electron configuration to change to a noble gas? BECAUSE IT’S STABLE!!!

Ions and Compounds Ionic Compounds When representative metal and nonmetals react, they transfer electrons in such a way that both the cation and the anion have noble gas electron configurations. Covalent Compounds When nonmetals react they share electrons in a way that leads to both atoms having noble gas electron configurations

Octet rule - every atom wants to have eight valence electrons, just like the nearest noble gas Duet rule – hydrogen only wants 2 valence electrons *one exception* - boron (B) – it only needs 6 valence electrons.

Predicting Compounds Chemical compounds are always electrically neutral. That helps up figure out formulas. Ex. Li + and F - => LiF Practice Fe 2+ and P 3- K + and S 2+ Mg and ClAl and O

Practice on your own What compound would form from these atoms? Ex. Li + and F - => LiF Rb and I C and Cl P and H C and O

Size Does Matter When atoms loose or gain electrons their relative size changes. Cations are smaller than parent atom Anions are larger than parent atom

Size Does Matter

Structure All the large anions get packed closely together. Forms rows and columns Small cations fill in the small spaces. Still in the same rows and columns.

Structure Ions are packed together to maximize the attractions between ions