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biology chapter 2
Terms in this set (28)
anything that has mass & occupies space
the amount of matter something contains
a pure substance that cannot be broken down by ordinary chemical means
2 or more atoms joined by chemical bonds
substance whose molecules contain atoms of more than one element
smallest unit of an element that has all the properties of that element
number of protons in the nucleus of an atom. Defines the element - is the same for every atom of that element
the number of protons plus the number of neutrons in the nucleus, can vary
atoms of the same element that differ only in the number of neutrons
- isotope with an unstable nucleus, the nucleus decays at a characteristic rate
- the time it takes for 50% of the radioactive atoms in a sample to decay
( valence ) electrons
Chemical properties of an atom depend only on its outer.......
union between the electron structures of atoms
The first energy level can hold.........
The next few energy levels can each contain
Chemical bonds: 3. Hydrogen bond - the weak attraction between the partially positive end of one polar molecule and the partially negative end of another . Weak and transient, but cumulative effects are extremely important
3. hydrogen bond
formed when two atoms of opposite charges ( ions) attract
formed when atoms share one or more pairs of electrons
attraction of an atom for the shared electrons of a covalent bond
the weak attraction between the partially positive end of one polar molecule and the partially negative end of another . Weak and transient, but cumulative effects are extremely important
a polar compound
polar compounds are.........
nonpolar compounds are.........
are responsible for all the biologically important properties of water.
Hydrogen bonds are responsible for all the biologically important properties of water.
1. water clings to other polar molecules cohesion- water molecules form H bonds with other water molecules adhesiom - water molecules form H bonds with other polar molecules
2. water stores heat and modifies temperature
3. water is a good solvent - for hydrophilic (polar and charged ) substances
4. water organizes nonpolar (hydrophobic) molecules
5. water ionizes - basis for the pH scale . Neutral pH = 7.0
any substance that adds hydrogen ions to solution ( pH< 7.0)
any substance that increases the hydroxide ions in solution ( pH >7.0)
measures the concentration of free hydrogen ions in solution
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