chapter 4 section 2 and 3. periodic trends how are elements arranged on the table? order of...

Chapter 4Chapter 4

Section 2 and 3Section 2 and 3

Periodic TrendsPeriodic Trends

How are elements arranged on the table?How are elements arranged on the table? Order of increasing atomic numberOrder of increasing atomic number

What is a trend?What is a trend? Predictable change in a particular direction Predictable change in a particular direction

Trends on the periodic table allow us to Trends on the periodic table allow us to make predictions about chemical behaviormake predictions about chemical behavior

Atomic RadiiAtomic Radii

Do we know the exact size of an atom?Do we know the exact size of an atom? No it is difficult to determineNo it is difficult to determine It is determined by the volume occupied by It is determined by the volume occupied by

the electrons surrounding the nucleusthe electrons surrounding the nucleus

Radii are usually determined for atoms Radii are usually determined for atoms that are chemically bonded or close that are chemically bonded or close together in the solid statetogether in the solid state


What is bond radius?What is bond radius? ½ the distance between the nuclei of the ½ the distance between the nuclei of the

atoms in each moleculeatoms in each molecule Line A represents twice the bond radiusLine A represents twice the bond radius

Van der Waals radius: Van der Waals radius: Distance between the nuclei in adjacent Distance between the nuclei in adjacent

nonbonded molecules, which is equal to twice nonbonded molecules, which is equal to twice the distance called the Van der Waals radiusthe distance called the Van der Waals radius


Which radius is used in this book?Which radius is used in this book? Bond radiusBond radius Van der Waals are not very precise Van der Waals are not very precise Measuring bond radius is a useful way to Measuring bond radius is a useful way to

compare the size of atomscompare the size of atoms

Atomic RadiusAtomic Radius

What is the trend for atomic radius on the What is the trend for atomic radius on the periodic table?periodic table?

The radii increases as you go down a groupThe radii increases as you go down a group Due to the addition of another energy level Due to the addition of another energy level

from one period to the next from one period to the next


Electron shielding:Electron shielding: Electrons in the inner energy level are Electrons in the inner energy level are

between the nucleus and the outermost between the nucleus and the outermost electronselectrons

The inner electrons shield the outer electrons The inner electrons shield the outer electrons from the full charge of the nucleusfrom the full charge of the nucleus

Since they are not subject to the full charge of Since they are not subject to the full charge of the nucleus they are not held as close to the the nucleus they are not held as close to the nucleusnucleus


What happens to the radius as you go What happens to the radius as you go across a period?across a period? The radius decreases as you go across a The radius decreases as you go across a

periodperiod

The radius decreases because the positive The radius decreases because the positive charge of the nucleus increasescharge of the nucleus increases• This causes the nucleus to pull the electrons closer This causes the nucleus to pull the electrons closer • This reduces the size of the atom This reduces the size of the atom • Eventually the electrons will not come any closer Eventually the electrons will not come any closer

and the size of the atom tends to level offand the size of the atom tends to level off

Ionization Energy, Electron Affinity, Ionization Energy, Electron Affinity, and Melting Pointsand Melting Points

Are atoms neutral or do they have a Are atoms neutral or do they have a charge?charge? Electrically neutral Electrically neutral Protons = ElectronsProtons = Electrons

Ionization energy:Ionization energy: Energy used to remove an outer electronEnergy used to remove an outer electron


If an atom loses an electron it becomes a If an atom loses an electron it becomes a _________ ion_________ ion

Positive ionPositive ion Alkali metals lose 1 electronAlkali metals lose 1 electron If you lose an electron the ion is smaller than If you lose an electron the ion is smaller than

the atom the atom Figure 4-25 page 138Figure 4-25 page 138


Which way does ionization energy Which way does ionization energy increase?increase? Increases across a periodIncreases across a period

• The electrons are held more tightly to the nucleusThe electrons are held more tightly to the nucleus

Decreases down a groupDecreases down a group• The outer electrons are held less tightly to the The outer electrons are held less tightly to the

nucleus and less energy is required to remove onenucleus and less energy is required to remove one

• Attractive forces between the nucleus and the Attractive forces between the nucleus and the electrons decreases and the energy required to electrons decreases and the energy required to remove an electron decreases remove an electron decreases

Electron AffinityElectron Affinity

Electron Affinity:Electron Affinity: Ability of an atom to attract and hold an Ability of an atom to attract and hold an

electronelectron An approaching element could feel the net An approaching element could feel the net

pull and enter the vacant orbitalpull and enter the vacant orbital

When Fluorine gains an extra electron it When Fluorine gains an extra electron it becomes a ___________ ion. becomes a ___________ ion. • Negative ion Negative ion • Figure 4-28Figure 4-28


What does a negative electron affinity What does a negative electron affinity indicate?indicate? Energy is released when an atom gains an Energy is released when an atom gains an

electronelectron

What does a positive electron affinity What does a positive electron affinity indicate?indicate? Energy is needed to add the electron to an Energy is needed to add the electron to an

atomatom


What is the trend for electron affinity?What is the trend for electron affinity?

It becomes more negative across a periodIt becomes more negative across a period Decreases from top to bottom in a groupDecreases from top to bottom in a group There are exceptions to these general trends There are exceptions to these general trends

Trends in Melting and Boiling PointTrends in Melting and Boiling Point

What is the trend for melting and boiling What is the trend for melting and boiling point?point? At first, as the # of electrons increases the At first, as the # of electrons increases the

melting and boiling points increasesmelting and boiling points increases This indicates stronger bondingThis indicates stronger bonding However, when the d orbital becomes half-However, when the d orbital becomes half-

filled the melting and boiling points decreasefilled the melting and boiling points decrease

HomeworkHomework

Page 142Page 142 1-14 due before notes1-14 due before notes

Section 2 - MetalsSection 2 - Metals

What one property distinguishes metals What one property distinguishes metals from nonmetals?from nonmetals?

Metals are excellent conductors of electricityMetals are excellent conductors of electricity

The most widely used metal to conduct The most widely used metal to conduct electricity is copperelectricity is copper

MetalsMetals

In general, poor electrical conductors are In general, poor electrical conductors are poor heat conductorspoor heat conductors

The mechanism by which electricity is The mechanism by which electricity is conducted must be closely connected with the conducted must be closely connected with the mechanism for conduction of heatmechanism for conduction of heat

Other Properties of MetalsOther Properties of Metals Tungsten has the highest melting pointTungsten has the highest melting point Most are strong and durableMost are strong and durable Aluminum and magnesium have a high strength-Aluminum and magnesium have a high strength-

to-weight ratio making them useful in to-weight ratio making them useful in constructionconstruction

Some are ductile and can be squeezed into a Some are ductile and can be squeezed into a wirewire

Some are malleable and can be hammered into Some are malleable and can be hammered into sheetssheets GoldGold

2 or more can be mixed together to make an 2 or more can be mixed together to make an alloyalloy

chapter 4 section 2 and 3. periodic trends how are elements arranged on the table? order of...

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