WHAT IS CHEMICAL BONDING? Section

Chemical Bonding What is chemical bonding?  There are 118 (or more) elements, which combine in millions of different ways to form compounds.  Compounds are more than one kind of atom chemically combined.  Chemical bonding is the combining of atoms to form new substances

Electrons and Energy Levels An atom has a positively charged nucleus containing protons and neutrons. (p + are positive, n 0 are neutral) Outside the nucleus is the electron cloud, which contains the negative electrons.  The atom itself is neutral, so the number of p + must equal the number of e

Electrons and Energy Levels The electron cloud has Energy levels and electrons are arranged in these levels.  The lowest or the first level can hold only 2 e-.  The second can hold only 8 e-.  The third can hold only 18e-.  The fourth can hold only 32e

Electrons and Energy Levels The electrons in the highest (outermost) Energy level are called valence electrons.  They determine how atoms will combine.  When the highest Energy level of an atom is full, those atoms are very stable and do not combine with other atoms by forming chemical bonds

Electrons and Energy Levels Remember that elements in the same family have the same number of valence electrons.  Family 18, the Noble Gases, all, except He, which has 2, have 8 valence electrons and do not react or combine with anything

Electrons and Bonding An atom will bond with another if bonding gives both atoms complete outermost Energy levels

IONIC BONDING Section

Ionic Bonding One way for atoms to become stable is to transfer electrons from one to the other.  This kind of bonding is called ionic bonding.  Ionic bonds are made from ions, which are atoms with a plus or minus charge.  Ions with a “-” charge are called anions.  Ions with a “+” charge are called cations

Ionic Bonding When atoms transfer electrons, one loses and one gains. Atoms that lose e- have a positive charge. Atoms that gain e- have a negative charge.  Ex: Na has 11p+ and 11e-, it loses 1e- giving it 11p+ and 10e-. This gives it a 1+ charge (Na + )

Energy for Ion Formation In order for an electron to be removed from an atom, its attraction to the nucleus must be overcome.  The process of removing electrons and forming ions is called ionization.  The energy needed for ionization is called the ionization Energy.  This Energy is low for atoms with only a few valence electrons, so they lose electrons easily

Energy for Ion Formation The ionization Energy for atoms with a lot of valence electrons is high. It is so high, in fact, that these atoms gain electrons instead of losing them. The tendency of an atom to attract electrons is called electron affinity

Energy for Ion Formation What ions would the following make?  K (it has only 1 valence e-, so it will lose it becoming K + ).  Ca (it has 2 valence e-, so it will lose them both becoming Ca 2+ ).  Ga = Ga

Polyatomic Ions Certain ions are made from atoms that tend to stay together, but they have a charge. These are called polyatomic ions. See figure 7-18 on page 186. Ions come together to form neutral molecules!!! (*compounds*)

Combining Ions Ions come together to form neutral molecules!!! (*compounds*). What compounds would form?  Ga 3+ and Nitrate (NO 3 1- )  Ga(NO 3 ) 3  Ca 2+ and Phosphate (PO 4 3- )  Ca 3 (PO 4 )

Section 5-3 COVALENT BONDS

Covalent Bonds Bonds that occur between atoms who neither lose or gain electrons easily.  In these cases, no electrons are transferred, only shared.  Bonds formed with shared electrons are called covalent bonds.

Covalent Bonds By sharing, each atoms fills up its outer most Energy level because the shared electrons are in the outermost Energy level of both atoms at the same time.  Ex: H 2 each H has 1 valence e-, each wants two so they can share their electrons and both be happy.

Electron Dot Diagrams Used to represent electron sharing. Also known as Lewis Dot Structures. These diagrams are chemical symbols with dots around it, representing the valence electrons.

Formation of Molecules A combination of atoms formed by a covalent bond is called a molecule which is the smallest part of a compound.  Compounds are represented by chemical formulas.  Subscripts tell how many atoms of each element.  Ex: H 2 O- 2 H and 1 O

Covalent Properties Covalently bonded solids have low melting points. (most) Some form network solids- very large molecules.  Ex: diamonds and sand- these have high melting points.

Section 5-4 METALLIC BONDS

Metallic Bonds A metallic solid is a solid made of only one element. These are made with metallic bonds.  In metallic bonds, the outer electrons of the atoms form a common electron cloud often called a “sea of electrons.”  Having this “sea of electrons” is responsible for many of the metal properties like malleability, ductility because the metal atoms can slide over one another easily, yet still be held together.  It also allows for easy conduction.

Section 5-5 PREDICTING TYPES OF BONDS

Predicting Bonds When the elements in the bond are on the Periodic Table will help you predict which kind of bond will form. Metals (when by themselves) will have metallic bonds. Compounds formed between elements that lose e- easily and those that gain e- easily will have ionic bonds.  Metals tend to lose easily.  Nonmetals tend to gain easily.  Bonds between the two tend to be ionic bonds.

Predicting Bonds Compounds formed between elements that have similar tendencies to gain electrons will have covalent bonds.  Bonds between nonmetals will be covalent.

Combining Capacity of Atoms The number of valence electrons determines how an atom will combine with other atoms. Knowing how many valence electrons an atom has helps you determine how many electrons it will gain or lose when it forms a compound. The number of valence e- an atom gains or loses is its oxidation number.  Ex: Na has 1 valence e-, it can lose 1 or gain 7. It will lose 1 giving it a 1+ charge. (Na 1+ ). Cl has 7 valence e-, it will gain 1, giving it a charge of Cl 1-.