Chapter 7 Atoms & Bonding

What is Chemical Bonding? Chemical Bonding (def) – the combining of atoms of elements to form new substances. The rules of chemical bonding are determined by the structure of the atoms involved in the bond.

Let’s Review a Little… Protons are positively charged and are located in the nucleus. Neutrons have no charge (neutral) and are located in the nucleus. Electrons are negatively charged and are located in the electron cloud surrounding the nucleus. The electron cloud has energy levels called shells.

Let’s Review a Little… Electron Shells K Shell – holds 2 electrons L shell – holds 8 electrons M shell – holds 8 electrons (Actually the M shell can hold up to 18 electrons, but you’ll learn more about that in chemistry…along with the N, O, P and Q shells…)

Let’s Review a Little… The outermost electron shell is called the valence shell. The number of electrons in the valence shell determines how the atom will bond with another atom. The electrons in the valence shell are called valence electrons.

Why do Atoms Bond? It is an atoms goal to be as stable as possible. For an atom to be stable, it must have a full outer shell. Once an atom’s outer shell is full, the atom is stable and it will not seek out another atom to bond with because it doesn’t need any more electrons – its outer shell is full.

Why do Atoms Bond? The electron arrangement of the outermost energy level of an atom determines whether or not the atom will form chemical bonds. For example, the noble gases do not form chemical bonds because their outer shells are full, so they are stable. They are known as inert gases.

Why do Atoms Bond? Atoms of elements other than the Noble Gas Family do not have filled outermost energy levels (shells). Because of this, they bond with other atoms to ensure that their outermost energy levels are full. There are a few ways that atoms are able to do this. This is chemical bonding.

Ne Atoms Want Stability!!! Octet Rule (Oct like octopus – 8 legs) most atoms form bonds in order to have 8 valence e- They want a full outer energy level like the Noble Gases! Ne Stability is the driving force behind bond formation!

1. Ionic Bonds Rule: electron = e- Ionic Bonds – (def) Bonding that occurs because of the transfer of electrons. Ions - charged atoms either neg (-) or pos (+) formed by transferring e- from a metal to a nonmetal The metal gives an e- and the nonmetal receives an e-.

1. Ionic Bonds Before After Is either atom’s outer shell full? Are their outer shells full now?

1. Ionic Bonds What holds the atoms together is their opposite charges. Remember, opposites attract!!!!

Important Vocabulary of Ionic Bonds You Should Know Ion – a charged atom (+ or -) Ionic Bonding – Involves the transfer of electrons to bond atoms, some atoms gain electrons and other atoms lose electrons. Ionization – the process of removing electrons and forming ions. Energy is required for this process to occur. Ionization Energy – the energy required to form ionic bonds. When an electron is removed from an atom, the atom absorbs energy When an electron is gained by an atom, the atom releases energy. Oxidation Number – the charge on the atom after it gains or loses electrons in the process of chemical bonding. Valence electrons – the number of electrons in the outermost shell of an atom. Electron affinity – the tendency of an atom to attract electrons.

A. Properties of Ionic Bonds Ions form a 3-D crystal lattice This is because the ions are arranged in a specific way due to the way opposite charges attract and same charges repel. NaCl

A. Properties of Ionic Bonds Crystal lattice gives ionic compounds great stability. (strong) Different shaped crystal lattices also give ionic compounds interesting crystal shapes. There are 6 basic crystal shapes. These shapes help geologists identify minerals because 1 of the 5 “must-have” properties of minerals is that they have a crystalline structure. Ionic compounds also tend to have high melting points.

2. Covalent Bond Covalent Bond – (def) – bonding in which electrons are shared rather than transferred. Co = both Valent = valence shell

2. Covalent Bond In covalent bonding, the positively charged nucleus of each atom simultaneously (at the same time) attracts the negatively charged electrons that are being shared. The electrons spend most of their time between the atoms The attraction between the nucleus and the shared electrons holds the atoms together.

Properties of Covalent Bonds (def) The combination of atoms formed by a covalent bond is a Molecule. Mole-cule means little lump. (Mole = lump, cule = small) A molecule is the smallest particle of a covalently bonded substance that has all of the properties of that substance. NH3 H2O Cl2

Electron Dot Diagrams Electron Dot Diagrams can be used to show how ionic and covalent bonds either transfer or share electrons. In an electron dot diagram: The chemical symbol represents the nucleus and all inner electron shells. The dots represent the number of valence electrons in the outermost electron shell (valence shell)

Electron Dot Diagrams Transferring e- (ionic bonds) Sharing e- (covalent bonds)

Electron Dot Diagrams These show the electron dot diagrams of some common elements

Comparison Chart IONIC COVALENT transferred from metal to nonmetal shared between nonmetals Electrons Melting Point high low Soluble in Water yes usually not yes (solution or liquid) Conduct Electricity usually no crystal lattice of ions, form crystalline solids molecules, odorous liquids & gases Other Properties

3. Metallic Bonds Metals are elements that give up electrons easily In a metallic solid, only atoms of that particular element are present (it is made of only one element) In a metallic bond, the outer electrons of the atoms form an electron cloud or a sea of electrons. All of the electrons become the property of all of the atoms so they can all fill up their outer shells.

3. Metallic Bonds Because of the “sea of electrons” that the metallic bond produces, metals have very special properties They are malleable They are ductile They conduct electricity very well. They have a high melting point.

Comparing the Types of Bonds Link to Dog Bone Bonding Analogy Ionic bonds: One big greedy thief dog! Covalent bonds:  Dogs of equal strength. Polar Covalent bonds: Unevenly matched but willing to share. Metallic bonds:  Mellow dogs with plenty of bones to go around.