trends of the periodic table. atomic radius - one half the distance between the nuclei of identical...
TRANSCRIPT
Trends of the Periodic Table
Atomic radius - one half the distance between the nuclei of identical
atoms that are bonded together
Atomic Radius Trend:
1. Down a group – atomic radii increasesThis happens because of the increased number
of energy levelsThe energy levels shield the electrons from the
attraction of protons in the nucleus 2. Across a period – atomic radii decreases
This happens because as more electrons are added to the same energy level
Those electrons are pulled closer due to the increased number of protons in the nucleus
Largest atomic radii – 87 franciumSmallest atomic radii – 9 fluorine
Valence electrons - the electrons found in the outermost energy level
• These are the electrons available to be gained, lost, or shared
• All atoms want 8 valence electrons or a full outer energy level
• Valence electrons determine the chemical properties of the atom
• The group number is the number of valence electrons
Atoms are neutral because there are equal numbers of both protons and electrons
• Sometimes atoms can gain or lose electrons to form ions • An ion is an atom or group of atoms that has a positive
or negative charge
• Losing electrons results in a positive ion called a cation
• Gaining electrons results in a negative ion called an anion
Cations• Metals (left side of the table) form cations
• Cations are smaller than their atom counterparts because they are losing an electron (and sometimes an energy level)
• More positive charges have a greater pull on less negative charges
Cation formation
Anions• Nonmetals (right side of the table) form
anions • Anions are larger than their atom counterparts
because they are gaining an electron • Less positive charges cannot pull in the greater
number of negative charges
Anion formation
Ionization Energy• Ionization energy is the energy required to
remove an electron from an atom • a low IE means it is easier to remove the electron • Atoms can lose an electron, to form an ion • They do this to achieve noble gas electron
configuration (or 8 valence electrons) • When an atom easily loses electrons, it is said to
be active • Metals tend to lose electrons
Ionization Energy Trend:
1. Down a group – ionization energy decreases • As the valence electrons are farther from the
nucleus, the atom gives them up with less energy 2. Across a period – ionization energy increase • As the number of valence electrons increases in
the same energy level, the atom is more resistant to giving up an electron (more energy)
Greatest IE – fluorine Least IE - francium
Electron affinity
• Electron affinity is the energy change required to gain an electron
(released energy is a negative value) • When an atom releases a lot of energy
it is said to be active • Nonmetals tend to gain electrons
(large energy change)
Electron Affinity Trend
1. Down a group – electron affinity decreases (slightly) • Distance from the positive nucleus decreases the pull
on the electrons 2. Across a period – electron affinity increases • As the number of valence electrons added to the
same energy level increases, the atom easily accepts another electron (to reach 8)
Greatest EA – fluorine Least EA – francium
Electronegativity
Electronegativity is the measure of the ability of an atom in a chemical compound to attract electrons • All values are based on fluorine • Fluorine is most electronegative atom - 4.0 • The trend decreases in either direction from
fluorine