Chapter 2 Flashcards
what is an element?
a substance that cannot be broken down to other substances by chemical reactions
what is a compound?
a substance consisting of two or more different elements combined in a fixed ratio
what are essential elements?
20-25% of the 92 natural elements; elements that an organism needs to live a healthy life and reproduce
what are trace elements
elements that are needed by organisms to survive but only in minute quantities
what is an atom?
smallest unit of matter that still retains the properties of an element
what are neutrons?
atoms with a neutral charge
what are protons?
atoms with a positive charge
what are electrons?
atoms with a negative charge
what is the atomic nucleus?
the center of an atom; where protons and neutrons are packed tightly together
what is a dalton?
a dalton is a unit of measurement for atoms and subatomic particles
what is an atomic number of an element?
number of protons, unique to the element; written as a subscript to the left of the symbol for the element
what is the mass number
the mass number of an element is the total number of protons and neutrons in the nucleus of an atom
what is an isotope?
atoms with the same number of protons but different number of neutrons
what is a radioactive isotope?
an isotope in which the nucleus decays spontaneously, giving off particles and energy
what is a half life
the time it takes for 50% of the parent isotope to decay
what is radiometric dating
scientists measure the ratio of different isotopes and calculate how many half lives in years have passed since an organism was fossilized or a rock was formed
what is energy?
energy is defined as the capacity to cause change for instance by doing work
what is potential energy?
energy that matter possesses because of its location or structure
what is a electron shell
electrons are found in different electron shells, each with a characteristic average distance and energy level
what are valence electrons
outer shell electrons
what is the valence shell
outermost shell
what is a orbital
three dimensional space where an electron is found 90% of the time
what are chemical bonds
attraction between atoms
what is a molecule
two or more atoms held together by covalent bonds
what is a single bond
a pair of shared electrons
what is a double bond
sharing two pairs of valence electrons
what is an atom’s valence
an atom’s bonding capacity
what is a nonpolar covalent bond
electrons are shared equally
what is a polar covalent bond
electrons are shared inequally
what are ions
oppositely charged atoms
what is a cation
positively charged atom
what is a anion
negatively charged atom
what is a ionic bond
cations and anions attract each other; electron is stripped
what is electronegativity
attraction of a particular atom for the electrons of a covalent bond
what is a ionic compound
compounds formed by ionic bonds; salts
what is a hydrogen bond
noncovalent attraction between a hydrogen and electronegative atom
what are van der Waals interactions
changing regions of positive and negative charge that enable all atoms and molecules to stick to one another
what are reactants
starting matierals
what are products
resulting materials
what is a chemical equilibrium
the point at which the reactions offset one another exactly
