Chemistry Chapter 6

• A molecule is a neutral group of atoms that are heldtogether by covalent bonds
• A chemical compound whose simplest units aremolecules is called a molecular compound
• The composition of a compound is given by its chemical formula
• A chemical formula indicates the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts
• A molecular formula shows the types and numbers of atoms combined in a single molecule of a molecular compound
• Most atoms have lower potential energy when they are bonded to other atoms than they have as they are independent particles
• The electron of one atom and proton of the other atom attract one another
• The distance between two bonded atoms at their minimum potential energy (the average distance between two bonded atoms) is the bond length
• In forming a covalent bond, the hydrogen atoms release energy. The same amount of energy must be added to separate the bonded atoms
• Bond energy is the energy required to break a chemical bond and form neutral isolated atoms
• When two atoms form a covalent bond, their shared electrons form overlapping orbitals
• Noble gas atoms are unreactive because their electron configurations are especially stable
• Other atoms can fill their outermost s and p orbitals by sharing electrons through covalent bonding
• octet rule: Chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest energy level
• Hydrogen forms bonds in which it is surrounded by only two electrons
• Boron has just three valence electrons, so it tends to form bonds in which it is surrounded by six electrons
• Main-group elements in Periods 3 and up can form bonds with expanded valence, involving more than eight electrons
• Electron-dot notation is an electron-configuration notation in which only the valence electrons of an atom of a particular element are shown, indicated by dots placed around the element’s symbol. The inner-shell electrons are not shown
• An unshared pair, also called a lone pair, is a pair of electrons that is not involved in bonding and that belongs exclusively to one atom
• A structural formula indicates the kind, number, and arrangement, and bonds but not the unshared pairs of the atoms in a molecule
• single bond is a covalent bond in which one pair of electrons is shared between two atoms
• double bond is a covalent bond in which two pairs of electrons are shared between two atoms
• Double bonds are often found in molecules containing carbon, nitrogen, and oxygen
• triple bond is a covalent bond in which three pairs of electrons are shared between two atoms
• Double and triple bonds are referred to as multiple bonds
• double bonds have greater bond energies and are shorter than single bonds
• Triple bonds are even stronger and shorter than double bonds
• When writing Lewis structures for molecules that contain carbon, nitrogen, or oxygen, remember that multiple bonds between pairs of these atoms are possible