The Periodic Table. Science 9-Mr. Klasz

Transcription

1 The Periodic Table Science 9-Mr. Klasz

2 The definition of an element Element: A pure substance made up of one type of particle, or atom. Each element has its own distinct properties and cannot be broken down into simpler substances by means of a chemical change. On the periodic table, each element is enclosed in a box and represented by a symbol.

3 Elements Today Scientist have discovered 90 naturally occurring elements, and created about 28 more which they have created. The elements, alone or in combinations, make up our bodies, our world, our sun, and in fact, the entire universe.

4 The earth s crust The earth s crust is made up of 10 elements in notable quantities, with oxygen composing 46.6%.

5 The Periodic Table

6 The periodic table The periodic table organizes the elements in a particular way. A great deal of information about an element can be gathered from its position in the period table. For example, 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. Understanding the organization and plan of the periodic table will help you obtain basic information about each of the 118 known elements.

7 Before the periodic table chemistry was a mess!!! No organization of elements. Imagine going to a grocery store with no organization!! Difficult to find information. Chemistry didn t make sense.

8 Creating the periodic table Mendeleev-The first draft! In 1869, Dmitri Ivanovitch Mendeléev created the first accepted version of the periodic table. He grouped elements according to their atomic mass, and as he did, he found that the families had similar chemical properties. Blank spaces were left open to add the new elements he predicted would occur.

9 Some problems with Mendeleev s periodic table. He left blank spaces for what he said were undiscovered elements. (Turned out he was right!) He broke the pattern of increasing atomic mass to keep similar reacting elements together.

10 Our current periodic table Mendeleev wasn t too far off. Now the elements are put in rows by increasing ATOMIC NUMBER, instead of atomic mass. The horizontal rows are called periods and are labeled from 1 to 7. The vertical columns are called groups are labeled from 1 to 18.

11 Atomic Symbols C Cu Carbon Copper All elements have their own unique atomic symbol. It can consist of a single capital letter, or a capital letter and one or two lower case letters. This symbol is international and independent of language.

12 Atomic Symbols cont. Many atomic symbols are the first letter of the element. Ex: Carbon=C Others are the first two letters. (Ex: Calcium=Ca) Others use two prominent letters. (Ex: Cadium=Cd) Still others use latin, greek or other language roots. Ex: Copper=Cu. This comes from cuprium (latin)

13 Rules for atomic symbols Whatever the reason for naming an element, the same rules apply: Only one capital letter If the symbol is two letters, it must be one upper and one lower case letter The exception to this rule are the newest of the synthetic elements which have three letter symbols, Uut for example

14 The atomic number Elements are organized on the table 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. This is always a whole number. For instance, hydrogen has 1 proton, so it s atomic number is 1. The atomic number is unique to that element. No two elements have the same atomic number.

15 The atomic mass The atomic mass is the weight of one atom of an element. It is equal to the number of protons, plus the number of neutrons

16 Determining the number of protons and neutrons an atom of an element has: The atomic number gives the number of protons To determine the number of neutrons: Round the atomic mass to get the mass number. Number of neutrons=mass number-atomic number. Take Helium for example: The atomic mass of helium is 4.003, which rounds to give a mass number of 4. The atomic number is 2, meaning that helium has 2 protons. # of neutrons=4-2=2 Helium has 2 neutrons

17 The metalloid staircase The periodic table is grouped into three main categories: the metals, non-metals, and metalloids A staircase like shape separates these groups

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19 Properties of Metals Metals are good conductors of heat and electricity. Metals are shiny. Metals are ductile (can be stretched into thin wires). Metals are malleable (can be pounded into thin sheets). A chemical property of metal is its reaction with water which results in corrosion.

20 Properties of Non-Metals Non-metals are poor conductors of heat and electricity. Non-metals are not ductile or malleable. Solid non-metals are brittle and break easily. They are dull. Many non-metals are gases. Sulfur

21 Properties of Metalloids Metalloids (metal-like) have properties of both metals and non-metals. They are solids that can be shiny or dull. They conduct heat and electricity better than non-metals but not as well as metals. They are ductile and malleable.

22 Periods The horizontal lines on the periodic table are called periods. You can remember this by the way we write sentences: from left to right with a period at the end. Elements in the same period do not have the same properties. They are organized in increasing atomic numbers.

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24 Groups/Families Vertical Rows on the periodic table are called groups or families. Every column is a group, while families may be one column, or several columns put together. They are called families because all elements in a family have similar properties, and reactivity. This is because they all share the same number of valance electrons. This means they can undergo the same kind of chemical reactions.

25 Valance Electrons Valance electrons are those on the outside shell. These are the electrons that other atoms can steal or give to, when they undergo a chemical reaction. For example, Phosphorus has 5 valance electrons.

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27 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 valance electron shell.

28 What is an incomplete valance shell? All elements want to have eight valance electrons-this is their happy place! The exceptions to this are Hydrogen and Helium that only want to have two because they are so small! Elements that have 8 valance electrons are very un-reactive. They are happy, and so they don t want to share with anybody else.

29 An Example Elements with 1 valance electron are very unstable, and very reactive. They have an almost empty valance electron shell, and want to get rid of it. Elements with 7 valance electrons are also very reactive. They have almost a complete valance electron shell, and want to complete it. Here, Sodium has 1 valance electron, while Chlorine has 7.

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33 How do we know how many electrons an atom of a particular element has? In an uncharged atom, the number of protons is equal to the number of electrons. Therefore, the number of electrons is given by the atomic number. After an element reacts, it can gain or loose electrons and produce what is called an ion. More on in grade 10. For example, Hydrogen has 2 electrons.

34 How do we know how many valance electrons an atom has? The number of valance electrons an element has depends on what group they fall into. The group number A s at the top of each column tells us how many valance electrons an atom of each element has. The only exception to this rule is Helium which has two electrons.

35 The families of the periodic table Group 1A Alkali metals Group 2A Alkali earth metals Group 3A Earth metals (Boron Family) Group 3-12 Transition Metals Group 4A Tetrels (Carbon Family) Group 5A Pnictogens (The Nitrogen Family) Group 6A Chalcogens (The Oxygen Family) Group 7A The Halogens Group 8A The Noble Gases Rare Earth Elements The Lanthanide Series and the Actinide Series

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37 Hydrogen A family all its own! Hydrogen belongs to a family of its own. Hydrogen is a diatomic, reactive gas. Hydrogen was involved in the explosion of the Hindenberg. Hydrogen is promising as an alternative fuel source for automobiles It s a gas at room temperature. It has one proton and one electron in its one and only electron shell. Hydrogen only needs 2 electrons to fill up its valence shell.

38 ALKALI METALS Group 1 The alkali family is found in the first column of the periodic table. Hydrogen is not a member, it is a non-metal 1 electron in the outer shell Soft and silvery metals Very reactive, especially with water Alkali metals are never found as free elements in nature. They are always bonded with another element. Conduct electricity

39 ALKALINE EARTH METALS Group 2 2 electrons in the outer shell White and malleable Reactive, but less than Alkali metals Conduct electricity Several of these elements are important mineral nutrients (such as Mg and Ca)

40 TRANSITION METALS Elements in groups 3-12 Good conductors of heat and electricity. Some are used for jewelry and construction. The transition metals are able to put up to 32 electrons in their second to last shell. Can bond with many elements in a variety of shapes.

41 Earth Metals- Boron Family Group 3A/13 3 electrons in the outer shell Most are metals Boron is a metalloid Aluminum metal was once rare and expensive, not a disposable metal.

42 Tetrels- Carbon Family Group 4A 4 electrons in the outer shell 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. Contains elements important to life and computers. Silicon and Germanium are important semiconductors.

43 Pnictogens- The Nitrogen Family Group 5A 5 electrons in the outer shell. They tend to share electrons when they bond. Contains metals, metalloids, and nonmetals. The nitrogen family is named after the element that makes up 78% of our atmosphere. Nitrogen and phosphorus are both important in living things. Most of the world s nitrogen is not available to living things. The red stuff on the tip of matches is phosphorus.

44 Chalcogens -The Oxygen Family Group 6A 6 electrons in the outer shell Contains metals, metalloids, and non-metals Reactive Oxygen is necessary for respiration. Many things that stink, contain sulfur (rotten eggs, garlic, skunks,etc.)

45 Halogen Family Group 7A 7 electrons in the valance shell Very reactive, volatile, nonmetals. They are so reactive because they only need 1 electron to fill their outermost electron shell. They react with alkali metals to form salts. The elements in this family are fluorine, chlorine, bromine, iodine, and astatine. Used as disinfectants and to strengthen teeth.

46 The Noble Gases Group 8A: Noble gases have a full valance shell -8 valance electrons. Noble Gases are colorless gases that are extremely un-reactive. The family of noble gases includes helium, neon, argon, krypton, xenon, and radon. All the noble gases are found in small amounts in the earth's atmosphere. Used in lighted neon signs Also known as rare gases or inert gases

47 Rare Earth Metals-The Lanthanide Series and the Actinide Series The two rows at the bottom of the periodic table comprise the rare earth metals. Some are radioactive The rare earths are silver, silvery-white, or gray metals. Conduct electricity