UNIT 1: ATOMS, ELEMENTS AND PERIODICITY Page 2 st 1 Ionization Energy The energy defined as the energy required to remove one mole of electrons, from one mole of gaseous atoms to produce one mole of gaseous ions. Related to nuclear charge (how many protons) and the shielding effect of the inner electrons. Note: shielding is related to the distance of the electrons from the nucleus Variations in ionization energy have to do with ½ full shells and moving from s to p orbitals Ionization energies get larger 1st < 2nd < 3rd Electronegativity The ability of an atom within a covalent bond, to attract electrons to itself. Non-metal elements attract electrons more than metals atoms Increases across a period and decreases down a group ATOMIC SIZE Size decreases across a period because nuclear charge increases – no extra shielding Size increases down a family – valence electrons enter new shells, away from the nucleus Cations – smaller than atom because they experience less electron-electron repulsion Anions – larger than atom because they experience more electron-electron repulsions (When comparing go down then across) Physical Properties Within A Group As ionization energy decrease, the reactivity increases EMPIRICAL FORMULA UNIT 1: ATOMS, ELEMENTS AND PERIODICITY Simplest whole number ratio of the atoms of each element in the compound GENERAL INFORMATION Atomic # = # of protons, # of electrons Atomic Mass = # of protons + # of neutrons Rows on Periodic Table – Periods Columns on Periodic Table – Families (Have same # of valence e- To calculate from mass data PERCENT COMPOSITION TO determine the percentage by mass, express the mass of each element as a percentage of the total mass of the compound If given the percent composition you can assume 100 grams % by mass = (mass of element in 1 mole of compound) / (molar mass of compound) x 100 Mass percent = (mass of solute/mass of solution) x 1-- Assume 100 g sample, the % by mass Find AM (from periodic table) % by mass/AM = # of moles Divide by the smallest Determine the Empirical Formula (Whole number Ratios) MOLECULAR FORMULA To find the molecular formula take the given MW and divide by the Molar Mass of the Empirical Formula. Multiple each element in the compound by the result. Ie. HO (EF) H2O2 (MF) THE MOLE ISOTOPES # of particles in 1 mole = 6.022 x 1023 Isotopes differ ONLY in the number of neutrons (same # of p+ & e-) Masses are expressed in amu Relative atomic mass is defined as the weighted average of the mass of all isotopes. 1 mole has a mass = Molar Mass # of moles = mass given/ Molar mass Used to detect isotopes Each line represents one isotope (yaxis = % abundance, x-axis = amu) (% abundance) (MM) + (% abundance) (MM) ATOMS & ELECTRONIC CONFIGURATION 3 isotopes Quantum Numbers n= principal l = orbital ( 0 = s, 1=p, 2=d, 3=f) ml = -l to l ms = +/- 1/2 (speed of light, wavelength, frequency,) MASS SPECTROSCOPY Electron configuration of ion, eliminate highest principal quantum numbers first PHOTOELECTRON SPECTROSCOPY COLOUMBS LAW : EFFECTIVE NUCLEAR CHARGE: You can increase the effective nuclear charge by adding protons, or decreasing electrons. The effective nuclear charge is the pull of the electrons towards the nucleus. ELECTRON REPULSION: add electrons, increase repulsion Ionization Energies Look for large jumps between the different ionization energies to determine the number of valence electrons 1 valence electron Paramagnetic- unpaired electrons Diamagnetic – paired electrons Isoelectronic Species – Elements that have same electronic configuration