Periodic Table of Elements

Transcription

1 Periodic Table of Elements

2 The Atomic Nucleus The nucleus is a small, dense region at the center of the atom. It consists of positive protons and neutral neutrons, so it has an overall positive charge. The nucleus is just a tiny part of the atom, but it contains virtually all of the atom s mass. The strong nuclear force holds together protons and neutrons in the nucleus and overcomes the electric force of repulsion between protons.

3 Electrons Outside of the nucleus, an atom is mostly empty space, with orbiting negative particles called electrons. Because opposite electric charges attract each other, negative electrons are attracted to the positive nucleus. Electrons are located at fixed distances from the nucleus, called energy levels. Electrons at lower energy levels, which are closer to the nucleus, have less energy. Only when a lower energy level is full are electrons added to the next higher energy level.

4 Mendeleev Teacher and chemist writing a chemistry textbook. He wanted to find a way to organize the 63 known elements so it would be easier for students to learn about them. He made a set of cards of the elements. On each card, he wrote the name of a different element, its atomic mass, and other known properties. Mendeleev arranged and rearranged the cards in many different ways, looking for a pattern. He finally found it when he placed the elements in order by increasing atomic mass (1869).

5 Key to the Periodic Table The periodic table organizes the elements according to their atomic number, usually found near the top of the square. The atomic number refers to how many protons an atom of that element has. For instance, hydrogen has 1 proton, so it s atomic number is 1. No two elements have the same atomic number. You can predict with reasonably good accuracy the physical and chemical properties of the element. You can also predict what other elements a particular element will react with chemically.

6 Atomic Mass Atomic Mass refers to the weight of the atom. It is derived at by adding the number of protons with the number of neutrons. This is a helium atom. Its atomic mass is 4 (protons plus neutrons). What is its atomic number?

7 Atomic Mass and Isotopes While most atoms have the same number of protons and neutrons, some don t. Some atoms have more or fewer neutrons than protons. These are called isotopes. An atomic mass number with a decimal is the total of the number of protons plus the average number of neutrons.

8 Valence Electrons Valence electrons are the electrons in the outer energy level of an atom. These are the electrons that are transferred or shared when atoms bond together. Shared electrons bind atoms together to form chemical compounds. They determine many of the properties of an element. That s because these electrons are involved in chemical reactions with other atoms.

9 Valence Electrons v=ioxxfahbixg

10 Let s Recap 1 What particles are INSIDE the nucleus? 2 What particles are OUTSIDE the nucleus? 3 How are elements on the periodic table arranged? 4 What does atomic mass refer to? 5 What are valence electrons?

11 Meet the Elements Video v=d0zion8xjbm

12 Properties of Metals Have relatively high melting points. This explains why all metals except for mercury are solids at room temperature. Good conductors of heat and electricity. Shiny. Ductile (can be stretched into thin wires). Malleable (can be pounded into thin sheets). A chemical property of metal is its reaction with water which results in corrosion.

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14 Properties of Non-Metals Examples: hydrogen, carbon, chlorine, & helium. Reactive nonmetals tend to gain electrons. This explains why they cannot conduct electricity, which is a flow of electrons. Not ductile or malleable. Solid non-metals are brittle and break easily. Dull. They have a relatively low boiling point, so many nonmetals are gases. Reactivity of nonmetals depends on the number of electrons in it s outer energy level.

15 Properties of Metalloids Ex. Silicon Metalloids have properties of both metals and non-metals. Solids that can be shiny or dull. Conduct heat and electricity better than non-metals but not as well as metals. Ductile and malleable. Metalloids may act either like metals or nonmetals in chemical reactions, depending on the number of valence electrons they have.

16 Metalloids v=r01hbzqsvl4

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19 Families Periods Columns of elements are called groups or families. Elements in each family have similar but not identical properties. For example, lithium (Li), sodium (Na), potassium (K), and other members of family IA are all soft, white, shiny metals. All elements in a family have the same number of valence electrons. Each horizontal row of elements is called a period. The elements in a period are not alike in properties. In fact, the properties change greatly across even given row. The first element in a period is always an extremely active solid. The last element in a period, is always an inactive gas.

20 Hydrogen The hydrogen square sits atop Family AI, but it is not a member of that family. Hydrogen is in a class of its own. It s a gas at room temperature. It has one proton and one electron in its one and only energy level,and only needs 2 electrons to fill up its valence shell. This means it is very reactive. As a result, it is found in nature only in combination with other elements.

21 Exploding Hydrogen Bubbles v=d49tzvf1gmy

22 Alkali Metals The alkali family is found in the first column of the periodic table. Atoms of the alkali metals have a single electron in their outermost level (1 valence electron). They are shiny, have the consistency of clay, and are easily cut with a knife. They are solids at room temperature. They are low in density, and some of them float on water.

23 Alkali Metals om/watch? v=uo0ckj0ub wm They are the most reactive metals. They react violently with water. Alkali metals are never found as free elements in nature. They are always bonded with another element. In order of reactivity, francium is the most reactive followed by caesium, rubidium, potassium, sodium and lithium.

24 What does it mean to be reactive? Elements that are reactive bond easily with other elements to make compounds. Some elements are only found in nature bonded with other elements. What makes an element reactive? An incomplete valence electron level. All atoms (except hydrogen) want to have 8 electrons in their very outermost energy level (This is called the rule of octet.) Atoms bond until this level is complete. Atoms with few valence electrons lose them during bonding. Atoms with 6, 7, or 8 valence electrons gain electrons during bonding.

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28 Alkaline Earth Metals The alkaline earth metals are six chemical elements in column (group) 2 of the Periodic table. They are, from least to most reactive: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

29 Alkaline Earth Metals Are very reactive because they readily give up their two valence electrons to achieve a full outer energy level (the most stable arrangement of electrons). Reactivity increases from the top to the bottom of the group. They are silvery or gray in color. They are also relatively soft and low in density. Examples include calcium, which is needed for strong bones, and strontium, which is used for making cement and other products.

30 Transition Metals Groups 3 12 of the periodic table. More than half of all elements are transition metals. They are typical metals, with properties such as a superior ability to conduct electricity and heat. They also have the metallic properties of luster, malleability, and ductility. They have high melting and boiling points, and high density. These are the metals you are probably most familiar with: copper, tin, zinc, iron, nickel, gold, and silver.

31 Transition Metals The compounds of transition metals are usually brightly colored and are often used to color paints. Transition elements have 1 or 2 valence electrons, which they lose when they form bonds with other atoms. Some transition elements can lose electrons in their next-to-outermost level. Include the only elements that produce a magnetic field. The lanthanides and actinides are the transition metals that are usually placed below the main part of the periodic table. Lanthanides are relatively reactive for transition metals, and actinides are radioactive.

32 Rare Earth Elements The thirty rare earth elements are composed of the lanthanide and actinide series. The lanthanide series can be found naturally on Earth. Only one element in the series is radioactive. The actinide series is much different. They are all radioactive and some are not found in nature. Some of the elements with higher atomic numbers have only been made in labs.

33 Boron Family The Boron Family is named after the first element in the family. Atoms in this family have 3 valence electrons. This family includes a metalloid (boron), and the rest are metals. This family includes the most abundant metal in the earth s crust (aluminum).

34 Carbon Family Atoms of this family have 4 valence electrons. This family includes a non-metal (carbon), metalloids, and metals. The element carbon is called the basis of life. There is an entire branch of chemistry devoted to carbon compounds called organic chemistry.

35 Nitrogen Family The nitrogen family is named after the element that makes up 78% of our atmosphere. This family includes nonmetals, metalloids, and metals. Atoms in the nitrogen family have 5 valence electrons. They tend to share electrons when they bond. Other elements in this family are phosphorus, arsenic, antimony, and bismuth.

36 Oxygen Family Atoms of this family have 6 valence electrons. Most elements in this family share electrons when forming compounds. Oxygen is the most abundant element in the earth s crust. It is extremely active and combines with almost all elements.

37 Halogens In group 17 Highly reactive nonmetals. They have 7 valence electrons, so they are very eager to gain one electron to have a full outer energy level. include solids, liquids, and gases at room temperature, and they vary in color.

38 Halogens

39 Noble Gases Group 18 Nonmetals Nonreactive (with eight valence electrons, their outer energy levels are full. The only exception is helium, which has just two electrons). Colorless and odorless Have low boiling points, explaining why they are gases at room temperature. Noble gases are used for balloons, light bulbs, and lighted signs.

40 The Octet Rule Because the noble gases are the least reactive of all elements, their eight valence electrons are used as the standard for nonreactivity and to explain how other elements interact. This is stated as the octet ( group of eight ) rule. According to this rule, atoms react to form compounds that allow them to have a group of eight valence electrons like the noble gases.