chapter 2.1

• elements: substances that cannot be broken down into simpler substances by chemical means
• atom: the smallest particle of a chemical element that can exist.
• 118 elements on the periodic table
• nucleus: the dense central part of an atom containing protons and neutrons
• proton: positively charged particles located in the nucleus
• neutrons: an electrically neutral particle in the neucleus of an atom
• electrons: negatively charged particles in the outer shell of an atom that have a relative mass of 0.0005
• atomic number: number of protons in an atom's nucleus, which determines the element's chemical properties
• atomic mass: total mass of an atom determined by protons + neutrons
• each proton and neutron have a mass of one
• an electron has negligible mass and charge
• the number of neutrons in atoms of a particular element can differ, changing its mass
• isotopes are atoms of the same element that have different numbers of neutrons
• an atom that has gained an electron is negatively charged
• an atom that has lost an electron is positively charged
• ions: electrically charged atoms
• orbital: a region in space where electrons can exist in a stable state, where they are not in direct contact with the nucleus
• maximum number of electrons in an orbital is 2
• shell: one or two more orbital zones within an atom where electrons occur, different shells have different energy levels
• after the first shell, the maximum number of electrons per energy level is 8
• subatomic particles: electrons, protons, neutrons, and neutrons
• atom is always electrically nuetral
• as you change the number of protons the element changes
• number of protons is the atomic number
• atomic number determines how the elements are arranged in the periodic table and how many protons an element has
• protons and electrons have to be equal in order for the element to be electrically nuetral
• electron cloud: cannot prediction its exact location, negative energy around the nucleus
• isotopes: atoms of the same element with different numbers of neutrons, used for predicting the age of samples
• isotopes occur with a change in the number of nuetrons (ionization)
• ionization: process of making an ion
• cation: a positively charged ion that has lost electrons and has a positive charge
• anion: a negatively charged ion that has lost electrons and is therefore positively charged
• energy level/shell that is closest to the nucleus is going to have the lowest energy
• potential energy is the energy stored in an object due to its position or shape.
• atoms with more than two electrons have multiple orbitals that differ in size, shape in distance form the nucleus
• an elements chemical reactivity depends on the degree to which its outermost shell is filled
• valence electrons: in the outermost shells, most energy and taking part in bond formation, valence shells.