Trends in the Periodic Table trend: direction or pattern p

s, p, d and f blocks of the periodic table

groups periods “ Long form ” periodic table

Electronic structures are related to the position of the elements on the periodic table –s-block: s orbitals are filled –p-block: p orbitals are filled, etc.

Zumdahl p. 322

Atomic number Increases from left to right (across periods) Increases from top to bottom (down groups)

Period number: number of energy levels containing electrons Group: same valence shell electron configuration

Group names 1: alkali metals (1 valence electron) 17: halogens (7 valence electrons) 18: noble gases (all electron shells filled, little chemical reactivity) periodicity: repeating of similar properties because of similar valence electron configuration

Important Groups

Physical Properties in the PTE

Atomic and Ionic Radii Atomic radius: half the distance between the nuclei of two touching atoms Increases going down a group –Additional filled energy levels of electrons Decreases going across a period –More electrons = increased attraction to positive nucleus

Increasing Atomic Radius

Atomic Radius Increases

Radius of an atom always decreases when it loses an electron (becomes a cation +) –A whole energy level may be lost, or –There is less electron-electron repulsion (pushing away) between the electrons in different energy levels The radius of an atom always increases when it gains an electron (becomes an anion -) –Increased electron-electron repulsion pushes the valence shell away from the nucleus.

Ionic radius examples K K + Cl Cl -

Ionization energy The amount of energy that is required to remove an electron from a gaseous atom Decreases going down a group –Valence electrons are further from the nucleus, less “pull” from the protons

Effective Nuclear Charge Charge exerted on each electron by the positively charged nucleus

Ionization Energy Increases going across a period –Electrons on the same energy level are more strongly “pulled” by the nucleus (which is increasing in positive charge)

Ionization Energy Increases

Electronegativity How strongly an atom attracts other electrons in a chemical bond (electron affinity) Decreases going down a group –Valence electrons are further from the nucleus, less “pull” from the protons –Atoms increase in radius Increases going across a period –Electrons on the same energy level are more strongly “pulled” by the nucleus –Atoms decrease in radius

Electronegativity Increases

Other Physical Properties Melting Point Boiling Point Density Types of bonds formed

Chemical Properties

Elements in the same group have similar chemical properties

Increasing atomic and ionic radii Increasing ionization energy Increasing electronegativity Increasing reactivity

Alkali metals Soft, malleable (can be shaped) metals Low melting points –Can only contribute one electron to a bond – easily broken Low density –Largest atomic radius in the period Very chemically reactive –One valence electron, easily lost, + ion Tarnish quickly Combine with O, Cl, Br to form ionic compounds

sodium potassium rubidium cesium (l)

All react with water to form a solution of metal hydroxide and hydrogen 2M(s) + 2H 2 O(l)  2M + (aq) + 2OH - (aq) + H 2 (g) M = alkali metal sodium potassium Reaction is alkaline (base)

What trend in reactivity did you see as we moved down the group?

Increasing atomic and ionic radii Increasing ionization energy Increasing electronegativity Increasing reactivity

Halogens Very reactive non-metals –Need only one electron to fill valence shell All exist as diatomic molecules –Cl 2, Br 2, I 2 (all colored) Slightly soluble in water – non-polar bonds

Halogens – colored diatomic molecules fluorinepale yellow gas chlorineyellow-green gas brominered-brown liquid iodine black-purple solid purple gas

X 2 (aq) + H 2 O(l)  H + (aq) + X - (aq) + HOX(aq) –X = halogen –HOX = acid Ex: Chlorine: HOCl (HClO: chloric acid), used as a bleach, toxic to microbes, treats water

all quite electronegative (high electron affinity) easily gain electrons to form anions –halide ions Ability to gain electrons decreases going down a group reactivity decreases going down a group

Halogens combine with metals to produce ionically bonded salts containing a halide ion. –white and soluble in water  colorless solutions –insoluble: lead and silver compounds yellow –lead(II) iodide: bright yellow precipitate

Test for a halide ion by adding nitric acid, then a solution of silver nitrate –a precipitate indicates Cl-, Br-, or I- compoundcolor AgFno precipitate AgClwhite, then purple/black in sunlight AgBroff-white AgIpale yellow

silver bromide used to print black and white photos silver chloride used to print black and white photos silver iodide used to “seed the clouds” to make it rain

Oxidant: In a reaction, a higher halogen will replace a lower halogen. NaCl(aq) + Br -  NaBr(aq) + Cl -  NaCl(aq) + Br - (aq)

Ionization Energy Increases Atomic Radius Increases Electronegativity Increases Metallic Character Increases

Your questions… Answered!

Q: Why don’t the electrons crash into the nucleus? A: Electrons have lots of their own energy. E=hf due to their position around the nucleus. Electrons are constantly moving, very fast. This kinetic energy overcomes the positive attraction of the nucleus.

A: How does temperature affect ionization energy? Q: Temperature has no affect on ionization energy. Heat is only powerful enough to change kinetic energy of a particle or molecule. Microwaves and radio waves can affect nuclear spin. Gamma rays and X rays can effect the nucleus and the inner electrons. Electricity does have an affect on ionization energy.

Q: How does temperature affect the movement of the subatomic particles, specifically electrons? A: Temperature does not have enough energy to affect subatomic particle movement, only molecule movement.

Q: Where does ionization energy come from? A: Electricity

Q: If there is just one electron in a p x orbital, can it be located everywhere, or just on one side of the orbital? A: It can be located anywhere. An orbital is an area of probability inside of which the electron will be found. Electrons are constantly moving very fast, and can be anywhere within their orbitals.

Q: Why does ionization energy increase going across a period? Why, oh Why?!? A: The effective nuclear charge DOES change on each valence electron! ENC=+1 ENC=+2

Mid-term Tuesday, April 22 –14:40-16:10 –Room 407 or questions – short answer or calculations –2 definitions Answer all parts of all questions No dictionary/translator Bring calculator, Periodic Table on test