Biology 1305 Chapter 2 Questions & Answers

Matter - ANSWERSAnything that has mass and takes up space Element - ANSWERSA substance that cannot be broken down into simpler substances Compound - ANSWERSA substance consisting of two or more elements in a fixed ratio. essential elements - ANSWERSA chemical element required for an organism to survive, grow, and reproduce. About 20-25% of the 92 natural elements are required for life. trace elements - ANSWERSessential elements that are required by an organism in only minute quantities Atom - ANSWERSthe smallest unit of matter that retains the properties of an element Neutrons - ANSWERSa subatomic particle with no charge and is found in the nucleus of an atom Protons - ANSWERSA subatomic particle that has a positive charge and that is found in the nucleus of an atom. Determines the elements identity. Electrons - ANSWERSa subatomic particle with a negative charge atomic nucleus - ANSWERSAn atom's dense central core, containing protons and neutrons. daltons - ANSWERSThe unit neutron mass and proton mass are measured in since they're identical. atomic number - ANSWERSthe number of protons in the nucleus of an atom mass number - ANSWERSthe sum of the number of neutrons and protons in an atomic nucleus atomic mass - ANSWERSthe atom's total mass, can be approximated by the mass number Isotopes - ANSWERStwo atoms of an element that differ in number of neutrons Radioactive isotopes - ANSWERSIsotopes that decay spontaneously, giving off particles and energy half-life - ANSWERSlength of time required for half of the radioactive atoms in a sample to decay radiometric dating - ANSWERSprocess in which scientists measure the ratio of different isotopes and calculate how many half-lives (in years) have passed since an organism was fossilized or rock was formed Energy - ANSWERSthe capacity to cause change potential energy - ANSWERSenergy that matter possesses because of its location or structure Valence electrons - ANSWERSelectrons in the outermost shell (valence shell) Orbital - ANSWERSThe three-dimensional space where an electron is found 90% of the time Chemical bonds - ANSWERSthe attractive forces that hold atoms together Covalent bond - ANSWERSthe sharing of a pair of valence electrons by two atoms