The Periodic Table

Organization

• Group/family = vertical column • Period = row

Grouping of elements

• Metals – most elements on the table, left side • Nonmetals – far right and hydrogen • Metalloids – along zig-zag line; divides metals and non-metals

Metals

• Good conductors of heat/electricity • Malleable (can be formed) • Ductile (made into wires) • Reflects light • High densities • High melting points • Most are solids at room temperature • Easily lose electrons • corrode

Nonmetals

• Not good conductors of heat/electricity • Dull • Brittle • Low melting points • Low densities • Are solids, liquids and gasses at room temperature • Tend to gain electrons

Metalloids

• Cross between metals and nonmetals • Solids at room temperature • Can be shiny or dull • Malleable • Ductile • So-so conductors (better than nonmetals, but not as good as metals) – Form semiconductors when bonded

Groups/families

• Group 1 – alkali metals – React with water to form alkalines (bases) – Very reactive; not found alone in nature, found as compounds – Very soft metals – Have one valence (outermost) electron

Groups/families

• Group 2 – alkaline earth metals – Also form alkalines with water – Also very reactive, so not found as pure elements in nature – Not as reactive as group 1 – Have 2 valence electrons

Groups/families

• Group 17 – halogens – Means “salt former” – Tend to form salts with group 1 elements – Most reactive of the nonmetals – Have 7 valence electrons

Groups/families

• Group 18 – noble gases – Very unreactive – All are gases at room temperature – Have a full set of valence electrons • Full set = 8, except for helium which has 2

Groups

• Groups 3 – 12: Transition metals – Can put more than 8 electrons in their outermost orbital – Can use the 2 most outer orbitals to bond (the others use only the outermost) – Can form ions with different charges

Development of the periodic table

• In 1865, John Newlands, an English Chemist, arranged the elements according to their properties and in order of increasing atomic mass.

• He noticed a pattern that repeated every 8 elements, so he called it the

law of octaves

Development of the periodic table (cont)

• Dimitri Mendeleev, in 1869, used this information and produced the first orderly arrangement of all 63 known elements.

• He arranged them in a similar way to Newlands and created the first periodic table.

• Mendeleev started a new row each time he noticed that the chemical properties of the elements repeated.

• He left gaps where he thought newly discovered elements should go and made predictions about these elements

Mendeleev’s table

Mendeleev’s predicted elements

Modern Periodic Table

• Elements did not always fit neatly on the table in order of atomic mass • Henry Moseley studied the x-ray spectra of 38 different elements • He noticed a pattern as the atomic mass increased • However, after further study, he realized that the correlation was to atomic number and not atomic mass.

• The table was arranged in increasing atomic number and any discrepancies from Mendeelev’s table disappeared

Modern Periodic Table (cont)

• Periodic Law: the principle of chemical periodicity.

– When elements are arranged according to their atomic numbers, elements with similar properties appear at regular intervals.

• This law works because of the pattern in the electron configuration of the elements.

– Elements in each column of the periodic table have the same number of valence electrons (electrons in their outer energy level)

Valence electrons

• Electron located in the outermost energy levels • Valence electrons are the ones that participate in chemical reactions.

• Elements with the same number of valence electrons tend to react in similar ways.

• This allows scientists to predict the properties and behavior of unknown elements.

Periodic trends

• Tells you how certain characteristics change as you move across and down the periodic table • 3 trends that we will look at: – Atomic radius – Ionization energy – electronegativity

Atomic radius

• The “size” of the atom • Decreases as you move from left to right across a row – Reason: as you move across a period, you add electrons to the atom in the same energy level. You also add protons to the nucleus, thus increasing the pull of the nucleus on the electrons, drawing them closer to the nucleus (effective nuclear charge) • Increases as you move down a column – Reason being is that when adding electrons, you add them in increasing energy levels, making the atom larger

Ionization energy

• The energy needed to remove an electron from an atom • Increases as you move across – Reason: effective nuclear charge increases requiring more energy to take them away (the outermost electrons are the first ones to be removed) • Decreases as you move down – Reason: the electrons that are added to increasing energy levels are further away from the nucleus, thus the attraction is decreased making it easier to take them away – Also, you have “electron shielding” which is when the inner electrons “shield” the outer ones from the pull of the nucleus

Electronegativity

• An atom’s desire to attract electrons • The more electronegative atom will take electrons away from a less electronegative atom (like a big brother takes toys from the little brother) • Increases as you move across – Reason: effective nuclear charge increases so electrons are attracted more strongly • Decreases as you move down – Reason: electron shielding decreases effective nuclear charge, decreasing the attraction

Natural Elements

• Only 93 of the elements on the periodic table occur in nature – Technetium (Tc) and Promethium (Pm) were detected in the stars, but not found on earth • Some elements can form through nuclear reactions (fusing of nuclei) – Center of stars – transmutations

Transmutations

• One element changes into another through a nuclear reaction –

NOT ALCHEMY

– Radioactive elements do this naturally – We have “created” synthetic elements using particle accelerators • cyclotron

Cyclotrons

• Speeds particles up to very high energies and then collides them – Nuclei of the particles fuse, creating “new” elements – Some of these are “superheavy” elements • Atomic number greater than 106 • Usually only a few nuclei are created, making it hard for scientists to study • They usually decay within a fraction of a second

Cyclotron at Berne, Switzerland

Cyclotron