Chapter 2 Flashcards
(40 cards)
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
