Elements and the Periodic Table

•Elements and the Periodic Table

• Classification is arranging items into groups or categories according to some criteria.

• The act of classifying creates a pattern that helps you recognize and understand the behavior of fish, chemicals, or any matter in your surroundings.

• These fish, for example, are classified as salmon because they live in the northern Pacific Ocean, have pinkish colored flesh, and characteristically swim from salt to fresh water to spawn.

• Classifying Matter

• Matter is usually defined as anything that has mass and occupies space.

• Metals and Nonmetals– A metal had the following properties.

• Metallic luster

• High heat and electrical conductivity.

• Malleability, able to be rolled or pounded into a thin sheet.

• Ductile, can be pulled into a wire.

– A nonmetal has the following properties• No metallic luster• Poor conductor of heat and electricity.• When it is a solid it is brittle so it cannot be pounded

or pulled into a wire.

• Most matter can be classified as metals or nonmetals according to physical properties. Aluminum, for example, is a lightweight kind of matter that can be melted and rolled into a thin sheet or pulled into a wire. Here you see aluminum pop cans that have been compressed into1,600 lb bales for recycling, destined to again be formed into new pop cans, aluminum foil, or perhaps aluminum wire.

• Solids, Liquids, and Gases– Gases have no defined shape or defined volume

• Low density

– Liquids flow and can be poured from one container to another

• Indefinite shape and takes on the shape of the container.

– Solids have a definite volume• Have a definite shape.

• (A)A gas dispenses throughout a container, taking the shape and volume of the container. (B) A liquid takes the shape of the container but retains its own volume. (C) A solid retains its own shape and volume.

• Mixtures and Pure Substances– A mixture has unlike parts and a composition that varies

from sample to sample– A heterogeneous mixture has physically distinct parts

with different properties.– A homogeneous mixture is the same throughout the

sample– Pure substances are substances with a fixed composition

• A classification scheme for matter.

– A physical change is a change that does not alter the identity of the matter.

– A chemical change is a change that does alter the identity of the matter.

– A compound is a pure substance that can be decomposed by a chemical change into simpler substances with a fixed mass ratio

– An element is a pure substance which cannot be broken down into anything simpler by either physical or chemical means.

• Sugar (A) is a compound that can be easily decomposed to simpler substances by heating. (B) One of the simpler substances is the black element carbon, which cannot be further decomposed by chemical or physical means.

• Elements

• Reconsidering the Fire Element– The phlogiston theory viewed phlogiston as a

component of all matter.– The burning of a material was considered to be the

escaping of phlogiston from the matter.– If a material did not burn, it was considered to contain no

phlogiston.

• The phlogiston theory. (A) In this theory, burning was considered to be the escape of phlogiston into the air. (B) Smelting combined phlogiston-poor ore with phlogiston from a fire to make a metal. (C) Metal rusting was considered to be the slow escape of phlogiston from a metal into the air.

• Discovery of Modern Elements– Antoine Lavoisier suggested that burning was actually a

chemical combination with oxygen.– Lavoisier realized that there needed to be a new concept

of elements, compounds, and chemical change.– We now know that there are 89 naturally-occurring

elements and at least 23 short-lived and artificially prepared.

• Priestley produced a gas (oxygen) by using sunlight to heat mercuric oxide kept in a closed container. The oxygen forced some of the mercury out of the jar as it was produced, increasing the volume about five times.

• Lavoisier heated a measured amount of mercury to form the red oxide of mercury. He measured the amount of oxygen removed from the jar and the amount of red oxide formed. When the reaction was reversed, he found the original amounts of mercury and oxygen.

• The number of known elements increased as new chemical and analytical techniques were developed.

• Names of Elements– The first 103 elements have internationally accepted

names, which are derived from:• The compound or substance in which the element was

discovered

• An unusual or identifying property of the element

• Places, cities, and countries

• Famous scientists

• Greek mythology

• Astronomical objects.

• Here are some of the symbols Dalton used for atoms of elements and molecules of compounds. He probably used a circle for each because, like the ancient Greeks, he thought of atoms as tiny, round hard spheres.

• The elements of aluminum, Iron, Oxygen, and Silicon make up about 88 percent of the earth's solid surface. Water on the surface and in the air as clouds and fog is made up of hydrogen and oxygen. The air is 99 percent nitrogen and oxygen. Hydrogen, oxygen, and carbon make up 97 percent of a person. Thus almost everything you see in this picture us made up of just six elements.

– Chemical Symbols• There are about a dozen common elements that have s

single capitalized letter for their symbol• The rest, that have permanent names have two letters.

– the first is capitalized and the second is lower case.• Some elements have symbols from their Latin names.• Ten of the elements have symbols from their Latin or

German names.

– Symbols and Atomic Structure• A molecule is a particle that is composed of two or

more atoms held together by a chemical bond.• Isotopes are atoms of an element with identical

chemical properties, but different masses due to a difference in the number of neutrons.

• The atomic mass of an element is the average of all the atomic masses of the isotopes.

– an isotopes contribution is determined by its relative abundance.

• Using information from the fixed mass ratios of combining elements, Dalton was able to calculate the relative atomic masses of some of the elements. Many of his findings were wrong, as you can see from this sample of his table.

• The mass of an element is the mass of the element compared to an isotope of carbon Carbon 12.

– Carbon 12 is assigned an atomic mass of 12.00 g.– 12.00 is one atomic mass unit

• The number of protons and neutrons in an atom is its mass number.

• Atomic numbers are whole numbers• Mass numbers are whole numbers• The atomic mass is not a whole number.

• A schematic of a mass spectrometer. The atoms of a sample of gas become positive ions after being bombarded by a beam of electrons. The ions are deflected into a curved path by a magnetic field, which separates them according to their charged-to-mass ratio. Less massive ions are deflected the most, so the device identifies different groups of particles with different masses.

• A mass spectrum of chlorine from a mass spectrometer. Note that that two separate masses of chlorine atoms are present, and their abundance can be measured from the signal intensity. The greater the signal intensity, the more abundant the isotope.

• The Periodic Law

• Dmitri Medeleev gave us a functional scheme with which to classify elements.– Mendeleev’s scheme was based on chemical properties

of the elements.– It was noticed that the chemical properties of elements

increased in a periodic manner.– The periodicity of the elements was demonstrated by

Medeleev when he used the table to predict to occurrence and chemical properties of elements which had not yet been discovered.

• Mendeleev left blank spaces in his table when the properties of the elements above and below did not seem to match. The existence of unknown elements was predicted by Mendeleev on the basis of the blank spaces. When the unknown elements were discovered, it was found that Mendeleev had closely predicted the properties of the elements as well as their discovery.

• The Periodic Law– Similar physical and chemical properties recur

periodically when the elements are listed in order of increasing atomic number.

• The Modern Periodic Table

• Introduction– The periodic table is made up of rows of elements and

columns.– An element is identified by its chemical symbol.– The number above the symbol is the atomic number– The number below the symbol is the rounded atomic

weight of the element.– A row is called a period– A column is called a family

• (A) Periods of the periodic table, and (B) families of the periodic table.

• Periodic Patterns– The chemical behavior of elements is determined by its

electron configuration– Energy levels are quantized so roughly correspond to

layers of electrons around the nucleus.– A shell is all the electrons with the same value of n.

• n is a row in the periodic table.

– Each period begins with a new outer electron shell

– Each period ends with a completely filled outer shell that has the maximum number of electrons for that shell.

– The number identifying the A families identifies the number of electrons in the outer shell, except helium

– The outer shell electrons are responsible for chemical reactions.

– Group A elements are called representative elements– Group B elements are called transition elements.

• Chemical Families– IA are called alkali metals because the react with water

to from an alkaline solution– Group IIA are called the alkali earth metals because

they are reactive, but not as reactive as Group IA.• They are also soft metals like Earth.

– Group VIIA are the halogens• These need only one electron to fill their outer shell

• They are very reactive.

– Group VIIIA are the noble gases as they have completely filled outer shells

• They are almost non reactive.

• Four chemical families of the periodic table: the alkali metals (IA), the alkaline earth metals (IIA), halogens (VII), and the noble gases (VIIIA).

• Metals, Nonmetals, and Semiconductors– Chemical behavior is determined by the outer electrons.

• These are called valence electrons

– These outer shell electrons are represented using electron dot diagrams.

– The noble gases have completely filled outer shells and are therefore stable.

• All other elements react so as to fill their outer shell and become more stable.

• Electron dot notation for the representative elements.

– When an atom or molecule gain or loses an electron it becomes an ion.• A cation has lost an electron and therefore has a

positive charge• An anion has gained an electron and therefore has a

negative charge.

– Elements with 1, 2, or 3 electrons in their outer shell tend to lose electrons to fill their outer shell and become cations.

• These are the metals which always tend to lose electrons.

– Elements with 5 to 7 electrons in their outer shell tend to gain electrons to fill their outer shell and become anions.

• These are the nonmetals which always tend to gain electrons.

– Semiconductors (metalloids) occur at the dividing line between metals and nonmetals.

• The location of metals, nonmetals, and semiconductors in the periodic table.

• (A) Metals lose their outer electrons to acquire a noble gas structure and become positive ions.  (B) Nonmetals gain electrons to acquire an outer noble gas structure and become negative ions.

• The periodic table of the elements.