Topic 3: Periodicity

Topic 3: Periodicity3.1 The periodic table

 3.1.1      Describe the arrangement of elements in the periodic table

in order of increasing atomic number3.1.2      Distinguish between the terms group and period

3.1.3      Apply the relationship between the electron arrangement of elements and their position in the periodic table up to z=20.

3.1.4      Apply the relationship between the highest occupied energy level for an element and its position in the periodic table.

 

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3.1.1.Describe the arrangement of elements in the periodic table in order of increasing atomic number.

Development of the Periodic Table

Dmitri Mendeleev Arranged elements by similar properties but left blanks for undiscovered elements (1869).

5

Henry Mosley Arranged the elements by increasing atomic number instead of mass (1913)

Elements arranged by increasing

atomic number into

periods (rows) and groups or families

(columns), which share similar characteristics

Groups or Families: Vertical Lines

Elements in the same group have similar chemical and physical properties!!

Why?• They have the same

number of valence electrons.

• They will form same kind of ions.

• Combine the same way

Family Names: Group 1: alkali metals Group 2: alkaline earth metals Transition metals Group 7: halogens Group 8/0: noble gases

Periods: horizontal row (7). Rows in the periodic table are called periods. 

As one moves from left to right in a given period, the chemical properties of the elements change.

Elements in the same row or period, have same number of energy levels.

11Na 13 Al 15P

Periodic Table & Electronic Configuration

13

ns1

ns2

ns2 n

p1

ns2 n

p2

ns2 n

p3

ns2 n

p4

ns2 n

p5 ns2 n

p6

d1 d5 d10

4f

5f

Ground State Electron Configurations of the Elements

Lewis Dot Diagram

Symbol of the element and dots representing the valence electrons

Na ● Ca ● ● Al ●

● ●

Shielding

Shielded slightly from the pull of the nucleus by the electrons that are in the closer orbitals.(inner e)

Effective Nuclear Charge

Effective nuclear charge is the charge felt by the valence electrons after you have taken into account the number of shielding electrons that surround the nucleus.(Effective nuclear charge is essentially the positive charge that a valence electron "sees“)

http://dl.clackamas.cc.or.us/ch104-06/efffective_nuclear_charge.htm

3.2 Physical properties  3.2.1      Define the terms first ionization energy and electronegativity3.2.2      Describe and explain the trends in atomic radii, ionic radii, first ionization energy, electronegativities and melting points for alkali metals (Li Cs) and the halogens (F I).3.2.3      Describe and explain the trends in atomic radii, ionic radii, first ionization energy, and electronegativities for elements across period3.2.4      Compare the relative electronegative values of two or more elements based on their position on the periodic table.

Video

http://www.youtube.com/watch?v=-4xKhr8RNjA

Atomic Size, Radii The electron cloud doesn’t have a definite

edge.

They get around this by measuring more than 1 atom at a time( diatomic)

Summary: it is the volume that an atom takes up

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/atomic4.swf

Group trends

As we go down a group (each atom has another energy level)

HLi

Na

K

Rb

Periodic TrendsThe atomic radius decreases as you go from

left to right across a period. Why? Stronger attractive forces in atoms (as you go

from left to right) between the opposite charges in the nucleus and electron cloud cause the atom to be 'sucked' together a little tighter. Remember filling up same energy level, little shielding occurring.

Na Mg Al Si P S Cl Ar

Ionic Size - Cations

Cations form by losing electrons.

Cations are smaller than the atom they come from.

.

Ca+2 < Ca

Ionic size - Anions

Anions form by gaining electrons. Anions are bigger than the atom they come

from.

N-3 > N

Periodic Trends Metals losing from outer energy level, more

protons than electrons so more pull, causing it to be a smaller species.

Non metals gaining electrons in its outer energy level, but there are less protons than electrons in the nucleus, so there is less pull on the protons, so found further out making it larger.

Li+1

Be+2

B+3

C+4

N-3O-2 F-1

Size of Isoelectronic ions Positive ions have more protons so they are

smaller.

Al+3

Mg+2

Na+1 Ne F-1 O-2 N-3

Electronegativity

Electronegativity

The tendency for an atom to attract electrons to itself when it is chemically combined with another element.

How fair it shares. Big electronegativity means it pulls the

electron toward it. Atoms with large negative electron affinity

have larger electronegativity.

Group Trend

The further down a group the farther the electron is away and the more electrons an atom has.

So as you go from fluorine to chlorine to bromine and so on down the periodic table, the electrons are further away from the nucleus and better shielded from the nuclear charge and thus not as attracted to the nucleus. For that reason the electronegativity decreases as you go down the periodic table.

Period Trend

Electronegativity increases from left to right across a period

When the nuclear charge increases, so will the attraction that the atom has for electrons in its outermost energy level and that means the electronegativity will increase

Period trend

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

Why? Elements on the left of the period table have 1 -2 valence electrons and would rather give those few valence electrons away (to achieve the octet in a lower energy level) than grab another atom's electrons. As a result, they have low electronegativity. Elements on the right side of the period table only need a few electrons to complete the octet, so they have strong desire to grab another atom's electrons.

Group Trend

electronegativity decreases as you go down a group. Why? Elements near the top of the period table have

few electrons to begin with; every electron is a big deal. They have a stronger desire to acquire more electrons. Elements near the bottom of the chart have so many electrons that loosing or acquiring an electron is not as big a deal.

This is due to the shielding affect where electrons in lower energy levels shield the positive charge of the nucleus from outer electrons resulting in those outer electrons not being as tightly bound to the atom.

Melting Points of Group 1

ElementElement Melting Point (K)Melting Point (K)

LiLi 453453

NaNa 370370

KK 336336

RbRb 312312

CsCs 301301

FrFr 295295

Metallic bonding Collective bond, not a single bond Strong force of electromagnetic attraction

between delocalized electrons (move freely). This is sometimes described as "an array of

positive ions in a sea of electrons

Why does the melting point decrease going down the alkali metals family?

Atoms are larger and their outer electrons are held farther away from the positive nucleus.

The force of attraction between the metal ions and the sea of electrons thus gets weaker down the group.

Melting points decrease as less heat energy is needed to overcome this weakening force of attraction.

Melting Points for halogens

ElementElement Melting Point (K)Melting Point (K)

FluorineFluorine 8585

ChlorineChlorine 238238

BromineBromine 332332

IodineIodine 457457

AstatineAstatine 610610

Why does melting point increase going down the halogens?

The halogens are diatomic molecules, so F2, Cl2, Br2, I2

As the molecules get bigger there are more electrons that can cause more influential intermolecular attractions between molecules.

The stronger the I.A, the more difficult it will be to melt. (more energy needed to break the I.A)

What are these I.A?

van der Waals forces (London dispersion): Electrons are mobile, and although in a

diatomic molecule they should be shared equally, it is found that they temporarily move and form slightly positive end and negative end.

Now that one end is + and the other -, there can be intermolecular attractions between the opposite charges of the molecules

van der Waals forces

IB requires knowledge specifically for halogens. Check out this site for more detail.

http://www.chemguide.co.uk/inorganic/group7/properties.html

Period 3 melting point trends

Explanation M.P rise across the 3

metals because of the increasing strength of the metallic bonds.

Silicon has a giant covalent structure just like diamond which makes its structure remarkably strong and therefore takes more energy to break apart.

The atoms in each of these molecules are held together by covalent bonds (except Ar)

They would have weak I.A affecting the amount of energy needed to melt them.

Ar has extremely weak forces of attraction between its atoms, so its easiest to melt.

3.3 Chemical properties

3.3.1 Discuss the similarities and differences in the chemical properties of elements in the same group.

3.3.2 Discuss the changes in nature from ionic to covalent and from basic to acidic of the oxides across period 3

Reactivity of alkali metals

Generally group 1 metals become more reactive as you go down a group.

The valence electron of group 1 are found further from the nucleus as you go down the group.

It is easier to remove an electron from francium than from lithium

Alkali metal + water

Li(s) + H2O (l) LiOH(aq) + H2 (g)(Li + and OH- in solution)

The metal reacts with water to form the hydroxide of the metal (strong base) and bubbles off hydrogen gas.

The larger the alkali metal, the more vigorous the reaction. Sometimes the H2 gas actually lights itself (exothermic reaction, releases heat) causing the H2 to burn.

MUST KNOW!

Na (s) + H2O (l) NaOH (aq)+ H2(g)

K (s) + H2O (l) KOH (aq)+ H2(g)

Alkali metals + halogens

2Na (s) + Cl2(g) 2NaCl (s) Halogens are good oxidizing agents, which

means they cause electrons to be lost from another atom (the reducing agent)

Halogens are 1 electron from stable octet and will try to remove electrons from valence electrons of other metallic atoms.

MUST KNOW!

2K (s) + Br2(l) 2KBr (s)

2Li (s) + I2(g) 2LiI (s)

Halogens reacting with halides

Halogens want an electron and even will remove electrons from other soluble salts, we refer to as halides.

When a salt dissolves it forms both of its ions in solution.

Ex: NaCl (aq) Na+(aq) and Cl- (aq) So halides are easily available for reactions

Done in aqueous systems

Chlorine is stronger OA (oxidizing agent) than bromine because its found higher on the periodic table, so Cl2 will remove the electron from Br-, making Cl- and Br2

Cl2 (aq) + 2Br- 2Cl- + Br2 (aq)

Cl2 (aq) + 2I- 2Cl- + I2 (aq)

Br2 (aq) + 2I- 2Br- + I2 (aq)

Properties of Metals Shiny (lustre) Good conductors of heat and electricity Malleable and ductile (change shape and make wires) Tend to lose electrons Metal oxides form basic solutions in water (pH greater than

7)

Properties of non-metals Brittle Poor conductors of heat and electricity Tend to gain electrons Non-metal oxides tend to be basic when dissolved in

water (pH less than 7)

Across Period 3: metallic to non-metallic oxides Basic solution from metallic oxide. Na2O(s) + H2O (l) 2 NaOH (aq) MgO (s) +H2O (l) Mg(OH)2 (aq) Hydroxides of group 1 and 2 generally considered

strong.

Acidic solution from non-metallic oxide. SO3(g) + H2O (l) H2SO4 (aq) P4O10 (s) + 6H2O (l) 4 H3PO4 (aq)Aqueous hydrogen involved with acidity

Properties of metalloids Based on chemical and physical properties Tend to have semi-conductive properties and

form amphoteric oxides. Considered metalloids are:

Boron (B) Silicon (Si) Germanium (Ge) Arsenic (As) Antimony (Sb) Tellurium (Te) Polonium (Po

Amphoteric Behave as an acid or a base depending upon

the reaction it is involved with. Also called amphiprotic (donate or accept a

proton, H+) Aluminum’s oxide is amphoteric.

Al2O3(s) + 3HCl (aq)→ AlCl3 (aq)+ 3H2O (l) Reacts with a strong acid to make a to make a salt

with water.

Al2O3(s)+ NaOH (aq) → NaAl(OH)4 (aq) Reacts with a strong base to form sodium aluminate