Chapter Four chemistry note

·         Noble gases don’t react because they have 8 valence electrons.

·         Compounds are the result of the formation of chemical bonds between two or more different elements. Ionic bonds occur when atoms of one element lose valence electrons and atoms of another element gain electrons. These bonds typically happen between metals and nonmetals.

·         In the formation of either an ionic bond or covalent bond, atoms lose, gain, or share, valence electrons to acquire an octet.

·         An atom is happiest with 8 valence electrons

·         Metals react with nonmetals

·         In ionic bonding, valence electrons of metals transfer to nonmetals because their ionization energies are low (groups 1A, 2A, and 3A). When they do this, they acquire the arrangement of noble gases (usually 8 valence electrons) and form IONS with positive charges.

·         Metals in ionic compounds lose their valence electrons to form positively charged ions called cations.

·         Nonmetals form negative ions when they gain valence electrons to attain an octet. Ions with negative charges are called anions.

·         If an atom loses an electron, the number of protons is greater and it becomes ionic. The new difference between protons and neutrons is the ionic charge.

·         The name of an anion uses –ide to replace the last syllable of the element name

·         Example: F + Li  

o   F has 9P and 10N in the nucleus, one layer with 2 electrons and an outer layer of 7 electrons

o   Li has 3P and 4N in the nucleus, one layer with 2 electrons and an outer layer of 1 electron

o   The one electron from Li goes over to F because it’s easier to move 1 than 7

o   The Li becomes a cation and the F becomes an anion

o   This would be an ionic bond because they are both stable

·         In ionic compounds, the attraction is very strong so the melting points are extremely high. At room temp, ionic compounds are solids.

·         The formula of an ionic compound indicates the number and kinds of ions that make it up. The sum of ionic charges in the formula is always zero.

·         Subscripts in the formula of an ionic compound represent the number of positive and negative ions that give an overall charge of zero. It means that ___ was needed to make a charge of zero. So if you have one element that has a greater charge than the other, you have to ass however many of the other element so make them equal out.

·         In the formula of an ionic compound, the cation is written first followed by the anion.

·         All polyatomic ions are negative except for ammonium.

·         Transition metals usually form two or more kinds of positive ions because they lose their outer electrons as well as electrons from a lower energy level. It is not possible to predict the ionic charge from the group number. They have a “variable valence”. A Roman numeral is used to match the ionic charge. Some metals that form more than one positive ion are:

o   Chromium (2 and 3), Copper (1 and 2), Gold (1 and 3), Iron (2 and 3), Lead (2 and 4), and Tin (2 and 4)

·         An ionic compound with 3 or more elements contains some type of polyatomic ion, which is a group of atoms that has an ionic charge. There is only one positively charge polyatomic ion: NH4⁺

·         No polyatomic ion exists by itself, it must be associated with ions of opposite charge, the bond is electrical.

·         When more than one polyatomic ion is needed for charge balance, parentheses are used to enclose the formula of the ion and a subscript is written.

·         Ionic compounds having two elements are named by naming the first element, followed by the second element, with an –ide ending. If more than one positive ion is possible, write a Roman numeral for the ionic charge following the name of the metal.

·         Covalent compounds are created because atoms of nonmetals have high ionization energies and do not lose electrons easily. The atoms are shared to achieve stability and molecules are formed. This satisfies the octet rule.

·         In Period 2, the number of electrons that an atom shares and the number of covalent bonds it forms are usually equal to the number of electrons needed to acquire a noble gas arrangement (satisfy the octet rule).

·         There are elements that exist as diatomic molecules (there has to be two of them): H, N, O, F, Cl, Br, I

·         If the first name is a metal than it’s ionic, otherwise it’s covalent.

·         Electronegativity is the attraction of an atom for valence electrons in a chemical bond. Nonmetals have higher electronegativity values because they have a greater attraction for electrons than nonmetals. Fluorine has the highest level. The values increase from left to right across each period and from bottom to top of each group.

·         Ionic bonding means electrons are transferred, covalent bonding means that electrons are shared.

·         A covalent bond between atoms with identical or very similar electronegativity values is a nonpolar covalent bond.

·         When electrons are shared unequally, the bond is a polar covalent bond. The shared electrons are attracted to the more electronegative atom, which makes it partially negative, while the atom with the lower electronegativity becomes partially positive. It has a separation of charges called a dipole.

·         When electronegativity differences are from 0.0 to 0.4, the electrons are shared about equally in a nonpolar covalent bond.

·         When the differences is greater than 0.4 but less than 1.8, the bond is a polar covalent.

·         Differences greater than 1.8 are ionic.

·         VSEPR (valence shell electron pair repulsion) theory indicates that electron groups will move as far apart as possible to reduce the repulsion between their negative charges.

·         A molecule with two or more polar bonds can be a nonpolar molecule if the polar bonds have a symmetrical arrangement in the molecule.

·         In a polar molecule, one end of the molecule is more negatively charged than another end. Polarity occurs when the polar bonds do not cancel each other out.

·         When a hydrogen atom is attached to highly electronegative atoms of fluorine, oxygen, or nitrogen, there are strong dipole-dipole attractions between the polar molecules. This type of attraction is called a hydrogen bond.

·         When writing compounds, the metal takes the number that is on top of the other element: Li⁺ and CO₃^2- = Li₂CO₃

o   Another example: Cu²⁺ and OH^- = Cu(OH)₂

o   ****don’t forget that polyatomics just get parentheses around them*****

·         Just remember:

o   To check and see if any of the compounds are polyatomic ions

o   Look at the ionic charge on your metal because that will become a subscript on your second part of the compound if the second part doesn’t have an exponent

o   If the second part does have an exponent, than it becomes a subscript on the metal (first part of compound) even if it’s a polyatomic

o   If it’s one of the transition metals with a Roman numeral, the Roman numeral becomes a subscript of the second part of the compound.