Chapter 6

The Periodic Table and Periodic Law

6.1 Development

Antoine Lavoisier (late 1700s) organized the 33 known elements (at the time) into a list with four categories

John Newlands (1864) noticed that when elements were arranged by increasing atomic mass, properties repeated every 8 elements

periodic pattern – the law of octaves

Meyer, Mendeleev, and Moseley 1869-Meyer and Mendeleev both saw a connection

between atomic mass and properties Mendeleev got more credit because he was first to

publish it Left holes of undiscovered elements Predicted properties of some undiscovered element- Sc, Ga,

Ge Still not completely correct

Mosley arranged his table by atomic number based on protons instead mass

fixed the problems with Mendeleev’s table

The Periodic Law The statement that there is a periodic

repetition of chemical and physical properties of the element when they are arranged by increasing atomic number.

horizontal rows are called periods vertical columns are called groups or families

The Modern Periodic Table

Groups 1A through 8A = Representative Elements (a.k.a Main) because they contain a wide range of chemical and physical properties

Groups 1B through 8B = Transition Elements

Classifying the elements• Metals

– shiny, smooth, clean, solid room temperature, good conductors of heat and electricity

• Alkali Metals= 1A (excluding hydrogen) – highly reactive

• Alkaline Earth Metals= 2A– highly reactive (not as much as 1A)

Classifying the Elements Continued…

Transition metals Group B elements contained in the D block of the

table Inner transition metals

the lanthanide and actinide series below the table

Classifying the elements continued

• Nonmetals=– Generally a gas or a

brittle, dull-looking solids

– Poor conductors

• Halogens=7A – REALLY REACTIVE

• Noble Gases= 8A – unreactive and stable

(all valence electrons are filled)

Classifying the Elements Continued…

Metalloids contains the physical and chemical

properties of both metals and nonmetal

6.2 Classification of the Elements The properties of each element in each group

are similar because they have the same number of valence electrons

The number of the group that the element is in = the number of valence electron (excluding the transition metals)

The energy level of an element’s valence electrons indicates the period on the periodic table

S,P,D, and F Blocks 4 different energy levels: s, p, d, and f S block= 1a and 2a

holds max of 2 electrons P block= 3A through 8A

max holds 6 electrons S block must fill before P block can fill Noble gases are stable because of filled S and P

blocks

S,P,D, and F Blocks Continued… D block = transition metals

max of 10 electrons

F block= inner transition metals unpredictable manner of filling max of 14 electrons

6.3 Periodic TrendsElectron clouds are fuzzy.So what does atomic size or radius mean?Ideas?

Atomic Radius

How it's normally done: Take a crystal of the pure element Find distance between adjacent nucleii

Atomic radius

Periodic Trends: Atomic RadiusDECREASES

INCREASES

Atomic Radius

Why do atomic radii increase as you move down a group?

Why does it decrease as you move across a period?

Atomic Radius• The increase from top to bottom is due to

adding electron shells.

• The decrease from left to right is due to increased nuclear charge as you move to the right, which draws electrons closer to the nucleus.

Ions

Atoms can gain or lose one or more electrons to form an ion.

An ion is an atom or a bonded group of atoms with a positive or negative charge.

Ionic Radius

an ion’s radius will be affected by its formation Would a cation (positive charge) be smaller or

larger than the corresponding neutral atom? Would an anion (negative charge) be smaller or

larger than the corresponding neutral atom? Explain ionic radii trends within periods and

groups.

Ionization Energy

Remember excited states of electrons? As energy level increases, distance from

nucleus increases Add enough energy, the electron is no longer

bound to the nucleus. Now, the atom has more protons than

electrons. What's its charge?

Ionization Energy

Periodic Trends: Ionization Energy

Ionization energy= energy required to remove an electron from a gaseous atom

Octet rule = atoms tend to gain lose or share electrons to acquire a full set of 8 valence electrons

Periodic Trends: Ionization Energy

INCREASES

DECREASES

Ionization Energy

Why does ionization energy tend to increase across a period?

Why does it tend to decrease down a group?

Periodic Trends: Electronegativity

Electronegativity= relative ability of an atom to attract electrons in a chemical bond.

Electronegativity Arbitrary units called Paulings (after Linus

Pauling) are used to express electronegativity.

Electronegativity increases from left to right across a period and from top to bottom down a group.

Why would these trends occur?

Periodic Trends: Electronegativity

INCREASES

DECREASES