2.2 Molecules and Chemical Bonds Flashcards
What are molecules?
groups of two or more atoms attached together that act as a single unit
What is a chemical bond?
any form of attraction between atoms that hold them together
What is the ability of atoms to combine with other atoms determined by?
largely in part by the electrons farthest from the nucleus, those in the outermost orbitals of the atom
What are valence electrons?
electrons in the outermost shell of an atom, they are at the highest energy level of the atom
What is a covalent bond?
results when two atoms share electrons
*figure 2.5 textbook
What is a molecular orbital?
a merged orbital formed when the outermost orbitals of two atoms come into proximity to each other and two atomic orbitals each containing one electron merge into a single orbital
What is a double bond?
two adjacent atoms sharing two pairs of electrons
four orbitals (each occupied by a single electron) merge to form two molecular orbitals
When do molecules tend to be most stable?
when the two atoms forming a bond share enough electrons to completely occupy the outermost energy level or shell
What is a polar covalent bond?
the resulting interaction when electrons are shared unequally between the two atoms
*figure 2.7 textbook
What does the unequal sharing of electrons result from?
a difference in the ability of the atoms to attract electrons aka electronegativity
What is electronegativity?
the ability of atoms to attract electrons
Describe the trend of electronegativity across a row in the periodic table.
- tends to increase across a row in the periodic table
- as the number of positively charged protons across a row increases, negatively charged electrons are held more tightly to the nucleus
ie. therefore oxygen is more electronegative than hydrogen and attracts electrons more readily than hydrogen
What is a nonpolar covalent bond?
a covalent bond between atoms that have the same, or nearly the same, electronegativity
the atoms share the bonding electron pair almost equally
Why are molecules held together by nonpolar covalent bonds important in cells?
they do not mix well with water
Describe an ionic bond.
forms between oppositely charged ions
- when an atom of very high electronegativity is paired with an atom of very low electronegativity, the difference in electronegativity is so great that the electronegative atom “steals” the electron from its less electronegative partner
- atom with the extra electron has a negative charge and is a negative ion
- atom that has lost an electron has a positive charge and is a positive ion
*figure 2.8 textbook
What happens when sodium chloride is placed in water?
the salt dissolves to form sodium ions that have lost an electron and so are positively charged, and chloride ions that have gained an electron and so are negatively charged
What happens when sodium chloride is in solution?
the two ions are pulled apart and become surrounded by water molecules
- negatively charged ends of water molecules are attracted to the positively charged sodium ion, and the positively charged ends of other water molecules are attracted to the negatively charged chloride ion
- only as water evaporates do the concentrations of Na+ and Cl- increase to the point where the ions join and precipitate as salt crystals
*figure 2.8 textbook
What is a chemical reaction?
process by which atoms or molecules called reactants, are transformed into different molecules called products
What can change in a chemical reaction?
chemical bonds that link atoms in molecules
What happens during a chemical reaction?
atoms keep their identity but change which atoms they are bonded to (bonds are broken and new bonds are formed)
*figure 2.9 textbook
What do chemical reactions do in biological systems?
chemical reactions provide a way to build and break down molecules for use by the cell, as well as to harness energy, which can be held in chemical bonds
