Introduction to Bonding Key Terms: Chemical Bond Ionic Bond Covalent Bond Electronegativity Metallic Bond

Why Form Bonds? Single atoms are not how most of the elements in nature exist Atoms “seek” the lowest energy state possible In the dissociated stated, aka individual atom state, most atoms are at a higher energy When the atoms combine it lowers the total energy of the system, which means it is more favorable

Chemical Bonds A chemical bond forms when 2 or more atoms rearrange valence electrons to increase stability Remember the term valence electron, what was considered a “magic number” of valence electrons? Most atoms prefer 8 valence electrons to fill their s- and p- orbitals Two ways for atoms to share electrons: Completely transfer Share the electron(s)

Octet Rule A chemical rule of thumb in which atoms that combine seek to have 8 electrons as their valence electrons An atom that is surrounded by 8 electrons that only contain s- and p-orbitals as valence orbitals will be stable

Ionic Bonding Ionic bonding forms when valence electrons are transferred from one atom to another When an ionic bond is present the compound is considered an ionic compound One of the most common examples of an ionic compound is that of common table salt, NaCl

Ionic Bonding

Anions and Cations Ionic compounds are comprised of: Cations- Anions- An atom or molecule that loses an electron to become positively charged Anions- An atom or molecule that gains an electron to become negatively charged

Properties of Ionic Compounds Ionic Compounds are arranged in crystal lattice structures to put the atoms in the lowest energy state possible Strong forces hold the ions together High melting and boiling points Hard- not easily crushed Conduct electricity when melted or dissolved because ions are free to move

Pure Water vs Salt Water If you are sitting in a pool of pure water and someone drops a plugged in toaster in with you. What will happen to you? Nothing Now, if someone adds salt to the pool before you get in what would happen once the plugged in toaster is added? Zap!

Covalent Bond A covalent bond occurs when electrons are shared when forming molecules Formation of molecules causes increased stability Covalent compound have weaker forces holding them together compared to that of ionic bonds

Properties of Covalent Bonds Covalent compounds have: Lower melting and boiling points Many covalent compounds are volatile liquids or gases Soft- easier to crush Are not conductors of electricity Ex. Methane is a covalently bound molecule that is a gas or a volatile liquid

Electronegativity Electronegativity is a property that tells how strong an atom’s attraction is for electrons Electronegativity is a property of an atom that can be found using a chart or table What do you think happens when one atom has a stronger pull on an electron than another? Think of a large dog and a smaller dog playing tug of war Unequal sharing

Polar Covalent Bonds Polar covalent bonds occur when electrons are shared unequally giving these molecules charged ends or poles Since oxygen has a higher electronegativity than hydrogen, oxygen holds onto shared electrons more, giving the oxygen a partial negative charge and the hydrogen a partial positive charge This type of unequal sharing is denoted by a ∂+ or ∂- to say slightly more positive or negative at that atom

Nonpolar Covalent Bonds Nonpolar covalent bonds occur when electrons are shared equally because the atoms have the same or close electronegativities Nonpolar compounds tend to have weaker interactions between molecules while polar compounds have stronger interaction between molecules This idea of molecules interacting with each other will be covered in a later lesson

Determining Bond Type Electronegativity Difference Type of Bond Greater than or equal to 1.7 Ionic bond Between 1.7 and 0.3 Polar Covalent Less than or equal to 0.3 Nonpolar covalent

Metallic Bond Metallic Bonds form in metals because the electrons are delocalized, giving metals a “sea of electrons” Due to this “sea” metals have the following properties Luster Conductors Malleable Ductile

Practice Problems Determine the type of bonds for the following compounds: Mg and F 4.0 – 1.2 = 2.8 ionic S and O 3.5 – 2.5 = 1.0 polar covalent Na and Cl 3.0 – 0.9 = 2.1 ionic N and O 3.5 – 3.0 = 0.5 (slightly) polar covalent B and F 4.0 – 2.0 = 2.0 ionic