PERIODIC TRENDS What are they? Properties we can predict from the periodic table Why are they? A few reasons explain them

Why do we care? So we know what's gonna go BOOM! Or what medicines will work Or how to make an iPod work Or how to make plastic Or how to make perfume… Or how to make food taste good etc.etc.etc. To figure out REACTIONS!

You will learn Why metals lose electrons Why non-metals gain electrons 2 periodic trends dealing with size 3 periodic trend dealing with electrons What causes the trends in groups What causes the trends in periods

LAW OF OCTETS Atoms tend to gain, lose, or share electrons to acquire a full outer energy level of either 2 or 8 electrons. Atoms want to have electron configurations like the noble gases. Atoms trying to acquire a full 1 st energy level are full with 2 electrons in the s orbital. Atoms trying to acquire a full outer energy level beyond the first, try for 8 electrons, the result of full s and p orbitals)

VALENCE ELECTRONS The electrons available to gained, lost, or shared in the formation of chemical compounds. They are often located in the incompletely filled main energy levels. They are in the s and p sublevels for the main group elements.

Ionic charges If electrons are lost, a positive ion is formed. – Metals If electrons are gained, a negative ion is formed. – Non-metals Group Val. El Ionic Charge 1+, 2+, 3+, 4+ or-, 3-, 2-, 1-, 0

WHAT ELSE AFFECTS TRENDS? Let’s use a magnet to illustrate the ideas. A magnet will provide a model for the nucleus with its positive charge, pulling on the electrons with their negative charges. Paper clips will represent electrons in energy levels.

How many paper clips can stick to a magnet, end to end? Why do they stick? The magnet pulls on the clips. What if you had a stronger magnet? It would pull harder on them or the magnet would pull them closer. What does this have to do with ATOMS and PERIODIC TRENDS?

The magnet represents the positive pull of the nucleus. This is called the NUCLEAR CHARGE…the positive charge of the nucleus, created by protons, pulling on the negative electrons. The more + protons there are, the stronger the nuclear charge. Note: The NUCLEAR CHARGE is NOT THE SAME as the charge on an ion that we talked about earlier. The NUCLEAR CHARGE is the POSITIVE CHARGE OF THE NUCLEUS FROM THE PROTONS.

What happened as you tried to add more? It’s harder to get them to stick. It’s easier to pull them off. Why? They are farther from the magnet so they don’t feel the force as strongly. Paper clips correspond to electrons in successive energy levels. As ENERGY LEVELS are added, each one is successively farther from nucleus, therefore affected less by NUCLEAR CHARGE. Electrons will be attracted less strongly.

Any other reason why the paper clips don’t stick as well? They are shielded by other clips…anything between magnet and clips reduces the effect of magnet Electrons in lower energy levels create SHIELDING. The presence of more electrons in the inner energy levels between the nuclear charge and valence electrons reduces the effect of nuclear charge on the outer valence electrons.

Trends that have to do with size: ATOMIC RADIUS (AR) <up and right IONIC RADIUS (IR) <up and right These trends DECREASE as you move UP A GROUP and OVER TO THE RIGHT THROUGH A PERIOD ATOMIC RADIUS: The size of the atom. One-half the distance between the nuclei of two identical atoms that are bonded together. IONIC RADIUS: The size of the ion.

Atomic radius

Trends that have to do with size: ATOMIC RADIUS (AR) <up and right IONIC RADIUS (IR) <up and right Group effect: Fewer energy levels as you go up…smaller Less shielding…more effect from pull of + nucleus Period effect: More protons, greater nuclear charge as you go right

Trends that have to do with electrons: IONIZATION ENERGY (IE) >up and right ELECTRON AFFINITY (EA) >up and right ELECTRONEGATIVITY (EN) >up and right These trends INCREASE as you move UP A GROUP and OVER TO THE RIGHT THROUGH A PERIOD IONIZATION ENERGY: The energy required to remove an electron from an atom to form an ion ELECTRON AFFINITY: The energy change when an electron is acquired by a neutral atom. ELECTRONEGATIVITY: A measure of the ability of an atom to attract electrons from another atom in a compound.

Trends that have to do with electrons: IONIZATION ENERGY (IE) >up and right ELECTRON AFFINITY (EA) >up and right ELECTRONEGATIVITY (EN) >up and right These trends INCREASE as you move UP A GROUP and OVER TO THE RIGHT THROUGH A PERIOD Group Effect: Fewer energy levels, closer to nuclear charge as you go up. Less shielding, fewer inner electrons between valence electrons and + pull of nucleus Period Effect: More protons, greater nuclear charge as you go right

Trends that have to do with size: < ATOMIC RADIUS (AR) <up and right IONIC RADIUS (IR) <up and right These trends DECREASE as you move UP A GROUP and OVER TO THE RIGHT THROUGH A PERIOD Trends that have to do with electrons: > IONIZATION ENERGY (IE) >up and right ELECTRON AFFINITY (EA) >up and right ELECTRONEGATIVITY (EN) >up and right These trends INCREASE as you move UP A GROUP and OVER TO THE RIGHT THROUGH A PERIOD

CATIONS t +charge Metals Lose electrons to acquire noble gas configuration. ION IS SMALLER THAN ATOM…WHY? Loss of outer energy level. Unbalanced + charge pulls electrons closer. ANIONS N -charge Non-metals Gain electrons to acquire noble gas configuration. ION IS LARGER THAN ATOM…WHY? Same outer energy level, but more electrons are added to it. + charge remains the same, but more – charge. More electrons repel each other more. Because of the Law of Octets…

Best metal, loses e - most easily lower left Fr Best non-metal, gains e - most easily upper right F METALLIC CHARACTER NON-METALLIC CHARACTER

SUMMARY 3 factors # of protons (nuclear charge) # of energy levels (size and distance from nucleus) # of inner electrons (shielding ) Trends that have to do with size: < ATOMIC RADIUS (AR) <up and right IONIC RADIUS (IR) <up and right Trends that have to do with electrons: > IONIZATION ENERGY (IE) >up and right ELECTRON AFFINITY (EA) >up and right ELECTRONEGATIVITY (EN) >up and right Metals lose electrons, and the + cations are smaller than the neutral atoms. Non-metals gain electrons, and the - anions are bigger than neutral atoms.