Periodic Table Chapter 5

Organizing the elements Section 1

Let’s Review! Chemical properties Any property that can only be tested by changing the chemical make-up of the substance. Physical properties Any property that can be tested without changing the chemical make-up of the substance Atomic mass Mass of protons and neutrons Atomic number Unique to each element, same as number of protons

Dmitri Mendeleev 1870, there were 63 elements known to man He organized them in order of their atomic mass, and saw a pattern from their properties. Was working on this while Thomson and Rutherford were still “exploring” the atom

Dmitri Mendeleev Arranged his table with repeating properties in columns, starting a new row each time the chemical properties repeated Left blank spaces in his table, concluding that these spaces were elements that hadn’t been discovered yet. Based on the patterns and the other elements around the blank space, he predicted the properties of those elements

What he called ekasilicon – it was discovered a few years later An Example What he called ekasilicon – it was discovered a few years later Prediction Atomic Mass 72 amu Density 5.5 g/mL Appearance dark gray metal Melting Point high melting point Germanium 72.6 amu 5.3 g/mL gray metal 937o C

Mendeleev’s Table

Dmitri mendeleev Some problems arose… A few elements appeared to be slightly out of place Mendeleev put them in the right place and said their atomic masses were incorrectly measured However, he was actually arranging them by the wrong number

Henry Moseley ~1910: Discovered atomic number He rearranged the periodic table by this number and it fell into perfect order Mendeleev’s table worked because as the number of protons increase, the atomic mass should increase, however if there are fewer neutrons it could decrease

Periodic Law Periodic Law: physical and chemical properties of the elements are periodic functions of their atomic numbers In other words, when the elements are arranged by their atomic numbers, you should see chemical and physical properties repeating themselves

Rows Left to right – called periods Elements in the same periods show a pattern As you move left to right, conductivity and reactivity change, and elements become less metallic

Columns Top to bottom – called groups Elements in a group have similar chemical properties The elements in the same group (column) have the same number of valence electrons

Exploring the periodic table Section 2

The periodic table is organized by atomic number Remember The periodic table is organized by atomic number For a neutral atom, the number of protons equals the number of electrons

Valence Electrons The trends found in a periodic table are a result of electron arrangement, specifically, the number of valence electrons Valence Electron: electrons in the outermost shell

Valence Electrons The group number of an element will tell you the number of valence electrons it has Group 1 elements: 1 valence electron Group 2 elements: 2 valence e- ’s Skip the middle Group 13 elements: 3 valence e- ’s Groups 14-18 elements: 4, 5, 6, 7, and 8 valence e- ’s respectively.

Why do we care about electrons?

Ion A neutral, stable atom will have equal protons and electrons When an atom gains/loses electron(s), the atom is no longer neutral and has a charge It becomes an ion Ion: a charged atom

Ion Ionization: When atoms EITHER gain or lose electrons All atoms want to have 8 valence electrons in the outer shell – this would make their outer shell full Elements that are really close to having 8 electrons, desperately want to get there, and tend to be the most reactive. Elements that are already “full” are considered inert, they don’t react because they don’t need to gain or lose electrons

Let’s Recall Protons = positive charge Electrons = negative charge p+ # CANNOT change, but e- # can So… If an atom GAINED electrons, would they be more positive, or more negative? If they LOST electrons?

Cation Remember…group 1 elements have 1 electron in their outer shell So…group 1 elements like to give up their single electron This would make it more POSITIVE We call this a cation

Anion Remember…elements in group 17 have 7 electrons in its valence shell (it would like 8) So…it will accept an electron from a “donor” This would make it more NEGATIVE We call this an anion

Let’s Practice Group 16 Give Up? or Gain? Group 13 Give Up? or Gain?

Charges How do we know if an atom is an ion? We show it with an exponent Cations have a +, and anions have a – If an atom has gained 3 electrons It is more negative = Al3- If an atom has lost 3 electrons It is more positive = Al3+

The Periodic Table It is divided into three major categories Metals Nonmetals Metalloids (semiconductors) These categories are based on general properties and are further broken down into families

Metals are left of the “staircase” Nonmetals are to the right Metalloids share properties of both

Metals Most elements are metals Like to give up their valence electrons Physical properties high luster (shiny), conductive (heat and electricity), malleable (bendable), ductile (stretchable), high density, high melting point All except Hg are solids at room temperature Chemical properties Most will react with oxygen

Nonmetals Like to gain electrons Physical properties dull, don’t conduct, brittle, low density, low melting points Like ashes (mainly carbon) Can be solid, liquid or gas at room temperature depending on the element.

Metalloids (Semiconductors) Share properties of both metals and nonmetals Can be shiny or dull, conduct ok, ductile and malleable or brittle These elements have become really important because of the computer revolution Computer chips are made out of semiconductors (normally Si) By position Al is a metalloid, but its properties make it a light metal

Families of elements Section 3

Families Families of elements have similar properties Each family also has the same number of valence electrons

Alkali Metals, Alkaline-Earth Metals, Transition Metals

Alkali Metals Group 1 (excluding H) 1 valence e- Very reactive, especially with water Soft, shiny white metals (can be cut with a knife!) Low density (Li, Na, and K float in water)

Hydrogen Hydrogen is in group 1 but is not an alkali metal, because it is only 1 proton and 1 electron (no neutrons) Its properties are closer to a nonmetals than to a metal it is a colorless, odorless, explosive gas with oxygen

Alkaline-Earth Metals Group 2 2 valence e- ’s Silver colored, more dense metals Not as reactive as alkali metals, but still very reactive metals. Magnesium is used in flash bulbs

Transition Metals Groups 3-12 1 or 2 valence e- ’s Most are silver in color Somewhat reactive These are most metals you are familiar with iron, gold, copper, zinc and nickel Since they are not that reactive they have more everyday uses.

Transition Metals Two bottom rows are the Lanthanide and Actinide series, sometimes called innertransition metals Lanthanide: also called rare- earth metals Actinide: very radioactive and not easily found in nature

Nonmetals Halogens, Noble Gases

Halogens Group 17/7a 7 valence e- ’s All nonmetals (can be solid, liquid or gas) Extremely reactive with alkali metals Chlorine is added to water as a disinfectant. The “chlorine” added to pools is a compound containing Chlorine, by itself chlorine is a green gas

Noble Gases Group 18/8a 8 valence e- ’s (except Helium) Full outer shell of electrons All are gases Extremely non-reactive (inert) All found in the atmosphere “Neon” lights contain a variety of Noble Gases

Other Nonmetals and Metalloids Groups 13-16 contain both nonmetals and metalloids Nonmetals: Oxygen, Nitrogen, Carbon, Sulfur, Phosphorus, and Selenium Metalloids: Boron, Silicon, Germanium, Arsenic Antimony, and Terellium The group is named by the first element in the column

Boron Group Group 13 3 valence e- ’s 1 metalloid, all others are metals All are solids at room temperature Aluminum is the most common it is actually the most abundant element on the planet.

Carbon Group Group 14 4 valence e- ’s 1 nonmetal, 2 metalloids, 2 metals all are solids Pure carbon can be diamonds, soot (ashes) or graphite. Silicon and germanium are used for computer chips Tin and lead are common metals

Nitrogen Group Group 15 5 valence e- ’s 2 nonmetals, 2 metalloids, 1 metal All but nitrogen are solids Nitrogen makes up 78% of the air Phosphorus is in several compounds (soaps) Arsenic is a well known poison

Oxygen Group Group 16 6 valence e- ’s 3 nonmetals, 2 metalloids except oxygen, all are solid Oxygen makes up 21% of the air it is necessary for things to burn sulfur is a yellow rock, that can burn.