Ch 2

• The four corners of an atomic symbol have specific uses. Top left: atomic mass. Top right: charge. Bottom left: atomic number. Bottom right: subscript
• Nunber of electrons (ion)= Z - charge of ion
• A= atomic mass
• Z= atomic number
• Number of neutrons: A - Z (atomic mass- atomic number)
• Atoms with the same number of protons but different numbers of neutrons are called isotopes.
• Radioactivity is also known as radioactive decay, and is a property of matter whereby an unstable nucleus emits small particles of energy in order to become stable
• An isotope with an unstable nucleus is called a radioactive isotope or radioisotope
• Subatomic particles include the electron/ beta, neutron, alpha, proton, and positron
• During radioactive decay, the nuclear mass and nuclear charge of the nucleus changes, resulting in a completely different element
• During radioactive decay, energy may also be released in the form of X-rays or gamma rays
• Mass spectrometry helped scientists to discover the charge to mass ratio of ions
• The pattern and intensity of the mass to charge ratios of ions is called a mass spectrum
• The atomic mass of an element is an average of the abundance of the isotopes that occur in nature
• Weighted average= (mass of isotope)(abundance of isotope)
• The lanthanide and actinide series is place below the periodic table
• Groups of elements: alkali metals, alkaline earth metals, transition elements, halogen, chalcogens, and noble gases
• Chemical reaction occur when atoms collide with another, therefore depend on valence electrons. This is why elements with similar electronic structures have similar chemical properties
• Isoelectronic refers to atoms and ions that have identical electron configurations
• Mercury and bromine are liquid under normal conditions
• Hydrogen, nitrogen, oxygen, fluorine and chlorine are gases at room temp
• Diatomic molecule acronym: P At Br I N Cl H O F S
• Metalloids exhibit properties of both metals and nonmetals
• Allotropes have distinct sets of chemical and physical properties. For example, oxygen and ozone are allotropes of oxygen
• The melting and boiling points of metals decreases down a group
• The melting and boiling points of nonmetals increases down a group
• Atomic radius decreases across a period due to an increase in the effective nuclear charge
• Atomic radius increases down a group due to an increase in number of energy levels
• Core electrons shield valence electrons from the strong nuclear force, however, valence electrons do not shield other valence electrons
• The ionization energy is the energy needed to remove an electron from an atom completely
• The first ionization energy decreases down a group but increases across a period
• Photoelectron spectrometers (PES) measure the kinetic energies of ejected electrons that are emitted due to the photoelectric effect
• Binding energy= energy of incoming photon - energy of emitted photoelectron
• Electron affinity is the energy change that accompanies the addition of an electron to an atom
• Some atoms readily attract electrons, and the electron affinity is negative, meaning that energy is released
• A positive electron affinity means that energy is added in order to attract an electron
• Fluorine has the highest affinity for electrons and francium has the lowest
• Electronegativity refers to the ability of an atom to attract electrons
• Cations lose electrons and are positive
• Anions gain electrons and are negative