The Modern Periodic Table Mendeleev and Mosley Mendeleevs

The Modern Periodic Table

Mendeleev and Mosley Mendeleev’s periodic table was ordered by increasing atomic mass: Did not work perfectly – some elements were out of order so they would fit in a family that had similar properties. Modern periodic table is ordered by increasing atomic number: Henry Moseley: scientist that determined an element’s atomic number (the number of protons in an atom). Hydrogen Atomic Number is 1, therefore it has 1 proton in the nucleus Potassium Atomic Number is 19, therefore it has 19 protons in the nucleus Radon Atomic Number is 86, therefore it has 86 protons in the nucleus When elements are arranged according to increasing atomic number, the elements fit perfectly in order from 1 - 118.

The Modern Periodic Table The modern periodic table consists of: Groups (1 -18): A vertical column of elements; also called a family Each group has similar physical and chemical properties Periods (1 -7): A horizontal row of elements. Each row identifies energy level and shell levels that Bohr had predicted.

The Modern Periodic Table Zig – Zag Line Group Period

Discussion Questions 1. Give the symbol, atomic number, and number of protons for each of the following elements: a) b) c) d) manganese magnesium arsenic astatine

Elements are classified as metals, non -metals, or semi-metals Three broad categories of elements shown on the periodic table: Metals Non-metals Semi-metals Elements of Groups 1, 2, and 13 to 18 are called main-group elements Elements in Groups 3 to 12 are called transition elements

Metals Property Characteristics Lustre Shiny Malleability Malleable (can be formed or shaped) Ductility Ductile (can be stretched into wire) Conductivity Good conductors of heat and electricity State Solid at room temperature (except mercury, which is liquid at room temp) Density Usually denser than non-metals Reactivity Active metals react with acid, very active metals react with water Boiling Point/Melting Point Usually have a high boiling point or melting point

Metals: Alkali Metal Alkali metals: Found in Group 1 (all elements, except hydrogen) Shiny and soft Highly reactive with water and oxygen (often stored in a non-reactive liquid such as oil)

Metals: Alkaline-Earth Metals Alkaline-earth metals: Found in Group 2 Shiny and soft (but not as soft as alkali metals) Highly reactive (but not as reactive as alkali metals) Magnesium (left) burns easily in air when ignited.

Non-metals Property Characteristics Lustre Dull in appearance Malleability Not malleable - likely to be brittle or shatter when struck Ductility Not ductile – cannot be stretched into wire Conductivity Poor conductors of heat and electricity State Often a gas at room temperature (except mercury, which is liquid at room temp) Density Usually have low density Reactivity Active metals react with acid, very active metals react with water Boiling Point/Melting Point Usually have a low boiling point and melting point.

Non-metals: Hydrogen: Usually on the left side of the periodic table Lightest element Colourless, odourless, tasteless Highly flammable Makes up over 90% of atoms in the universe On Earth: Most hydrogen is found combined with oxygen as water

Non-metals: Halogens: Found in Group 17 Highly reactive (therefore usually found in nature as part of compounds)

Non-metals: Noble Gases Noble gases: Found in Group 18 Odourless, colourless gases Least reactive of all of the elements Helium and neon never form compounds. Other noble gases form compounds with great difficulty.

Semi-Metals Semi-metals: Also known as metalloids Found in the green boxes in a staircase shape Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium, Polonium and Astatine. Have physical and chemical properties of both metals and non-metals Shiny (like metals) Brittle and not ductile (like non-metals) Poor conductors of heat and electricity (like non-metals)

Semi-metals: Silicon: Second-most abundant element in Earth’s crust (after oxygen) Used in many electronic devices (computers, smartphones) Used to make silicone (material used in cookware, contact lenses, prosthetics)

Transition Metals Groups 3 – 12 are the transition metals. These metals have a moderate range of reactivity and a wide range of properties. In general they are shying and good conductors of heat and electricity. They also have higher densities and melting points than groups 1 & 2. Transition Metals

ATOMIC SIZE Atomic size decreases moving left to right across a period. Elements have increasing numbers of electrons across a period. Number of valence shells stay the same across the period, but the number of protons in the nucleus increases. As such the protons pull the electrons closer to the nucleus and making the radius smaller. As you move down the families (each group) the atomic radius of the atom increases, this is because there are more electron shells, and that makes the atom larger.

ATOMIC SIZE

Periodic Trends/Patterns 1) Elements are arranged by atomic number – this number identifies how many protons and electrons are in the atom. 2) They are arranged into column’s called groups or “families. ” These families have similar physical and chemical characteristics. 3) The rows are called periods and they identify the energy level for the elements in that row. 4) The periodic table is divided into metals, semi-metals, and non-metals. The zig-zag line helps us understand where this divide is. 5) Elements in groups 1, 2, and 17 are quite reactive. Elements in group 18, the noble gasses, are very stable. 6) We can use the atomic mass, subtract it from the atomic number, and we can solve for how many neutrons are in the elements. 7) The ion charge will tell us how many electrons an element in ionic form will have. 8) Atomic size decreases across the period but increases down the group. 9) Each period adds one more electron shell (a new energy level). Period 1 has one electron shell, period 2 has two electrons shells and so on. (Will discuss in more detail later)

Assignment Page 192 Questions 9 -11, 13. Page 217 Questions 1 – 5, 6 -15 and, Worksheet Questions