Periodic Trends Ch# 6 in text

• An element’s properties are related to electron arrangement • An element’s location on the PT predicts many properties.

–Atomic radius –Ionic Size –Ionization energy –Electronegativity –Chemical reactivity

Periodic Trends

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Atomic radius

• Atomic radius of an atom is defined by the edge of its last energy level.

–However, this boundary is fuzzy • An atom’s radius is the measured distance identical atoms chemically bonded together between the nuclei of 2 divided by 2 .

Periodic Trends

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Atomic radius

• As we examine atomic radius from left to right across the PT we see a grad-ual decrease in atomic size .

– As e are added to the s and p sublevels in the same energy level, they are gradually pulled closer to the highly positive nucleus • The more e ’s in the atom the less dramatic this trend looks

Periodic Trends

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Atomic radius

• The change in atomic radii across the PT is due to e -

shielding

or to the effective nuclear charge – As we move across the PT we are adding e into the same general vol. in which case they will shield or interact with each other ( repulsion )

Periodic Trends

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Atomic radius

–We are also adding protons into the nucleus which increases the p + -e interaction (attraction) • So the nucleus gains strength while the e aren’t gaining much distance, so the atom is drawn in closer and closer to the nucleus.

–Decreasing the overall radius of the atom

Periodic Trends

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Ionic radius

• How does the size of an atom change when electrons are added or removed?

As an Atom loses 1 or more electrons (becomes positive ), it loses a layer therefore, its radius decreases.

Periodic Trends

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Ionic radius

• How does the size of an atom change when electrons are added or removed?

As an Atom gains 1 or more electrons ( negative ), it fills its valence layer, therefore, its radius increases.

Periodic Trends

• Elements in a group tend to form ions of the same charge.

–Modeled by electron configurations.

Periodic Trend of Ionic Charges

Tend to gain electrons to become negative Tend to lose electrons to become positive

Periodic Trends

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Ionization energy

• Another periodic trend on the table is ionization energy (a.k.a. potential) –Which is the energy needed to remove one of an atoms e s.

–Or a measure of how strongly an atom holds onto its outermost e s (

Valence electrons

) .

• If the e s are held strongly the atom will have a high ionization energy

Periodic Trends

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Ionization energy

• The ionization energy is generally measured for one electron at a time • You can also measure the amount of energy needed to reach in and pluck out additional electrons from atoms.

– There is generally a large jump in energy necessary to remove additional electrons from the atom.

the amount of energy required to remove a 2p e – (an e in a full sublevel) from a Na ion is almost 10 times greater than that required to remove the sole 3s e -

Periodic Trends

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Ionization energy

• There is simply not enough energy available or released to produce an Na 2+ ion to make the compnd NaCl 2 – Similarly Mg 3+ and Al 4+ require too much energy to occur naturally.

• Chemical formulas should always describe compounds that can exist naturally the most efficient way possible

Periodic Trends

• An atoms ability to lose an e e or gain an can be used to understand the Octet Rule • Octet Rule: atoms tend to gain, lose, or share electrons in order to acquire a full set of valence electrons .

–2 e e – in the outermost s sublevel + 6 in the outermost p sublevel= a full valence shell

Periodic Trends

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Electronegativity

• Electronegativity is a key trend.

–It reflects the ability of an atom to attract electrons in a chemical bond.

–F and it decreases moving away from F.

is the most electronegative element • Electronegativity correlates to an atom’s ionization energy and electron affinity

Reactivity

Reactivity

refers to how likely or vigorously an atom is to react with other substances. This is usually determined by how easily electrons can be removed ( ionization energy ) and how badly they want to take other atom's electrons ( electronegativity ) because it is the transfer/interaction of electrons that is the basis of chemical reactions. Metals

Metals

Period

-

reactivity

decreases as you go from left to right across a period.

Group

-

reactivity

go down a group increases as you Why? The farther to the left and down the

periodic

chart you go, the easier it is for electrons to be given or taken away, resulting in higher

reactivity

.

Non-metals

Period

-

reactivity

increases as you go from the left to the right across a period.

Group

-

reactivity

down the group. decreases as you go Why? The farther right and up you go on the

periodic table

, the higher the electronegativity , resulting in a more vigorous exchange of electron.