Warm Up How can all of earth’s material be broken down into elements? What elements do you think are the most abundant in the human body? Name at least one element that exist as a solid. A gas.

The elements

The Greeks were the first to explain why chemical changes occur. They proposed that all matter was composed of four substances: fire, water, earth, and air. All material on earth can be broken down into 100 different elements.

How can so few elements make up millions of known substances? Compounds are made by combining atoms of the various elements, just as words are constructed from the 26 letters of the alphabet.

The Elements All of the materials in the universe can be chemically broken down into about 100 different elements. Compounds are made by combining atoms of the elements just as words are constructed from the letters in the alphabet. Words Compounds

A. Abundances of Elements The elements in living matter are very different from those in the earth’s crust. In the human body, oxygen, carbon, hydrogen and nitrogen are the most abundant elements.

A. Abundances of Elements Nine elements account for about 98% of the earth’s crust, oceans and atmosphere.

Elements in the Universe These are the ten most common elements in the Universe as measured in parts per million, by mass [Wiki]: Element Parts per million Hydrogen 739,000 Helium 240,000 Oxygen 10,700 Carbon 4,600 Neon1,340 Iron1,090 Nitrogen950 Silicon650Magnesium580Sulfur440All Others650

Element can have several meanings Microscopic form Single atom of that element Element Macroscopic form Sample of that element large enough to weigh on a balance Element Generic form When we say the human body contains the element sodium or lithium, we do not mean that free elemental sodium or lithium is present. Rather we mean that atoms of these elements are present in some form. Element

B. Names and Symbols for the Elements Each element has a name and a symbol. The symbol usually consists of the first one or two letters of the element’s name. Examples: Oxygen O Krypton Kr Sometimes the symbol is taken from the element’s original Latin or Greek name. Examples: gold Au aurum lead Pb plumbum

Element Song http://www.privatehand.com/flash/elements.html http://education.jlab.org/elementflashcards/index.html

Trace metals Trace metals are metals in extremely small quantities, almost at the molecular level, that reside in or are present in animal and plant cells and tissue. They are a necessary part of good nutrition, although they can be toxic if ingested excess quantites. Trace metals include iron, magnesium, zinc, copper, chromium, nickel, cobalt, vanadium, arsenic, molybdenum, and selenium

Compounds composed of 2 or more elements in a fixed ratio properties differ from those of individual elements EX: table salt (NaCl)

B. Formulas of Compounds A compound is represented by a chemical formula in which the number and kind of atoms present is shown by using the element symbols and subscripts. Example: the simple sugar, glucose

HOW SMALL IS AN ATOM? At sea level and at 32oC, one cubic centimeter of air (that is, a space about the size of a sugar cube) will contain 45 billion billion molecules. Image a line -. Now divide that into 10,000 equal widths. Each width is a micron. Take a micron and divide it a million times. That’s the size of an atom.

Atoms Get Around Every atom you possess has almost certainly passed through several stars and been a part of millions of organisms on its way to becoming you. We are each so atomically numerous and so vigorously recycled at our death that a significant number of our atoms probably belonged to Shakespeare. Half a million atoms are lined up shoulder to shoulder could hide behind a human hair

18th Century Thoughts 1) Most natural materials are mixtures of pure substances 2) pure substances are either elements or a combo of elements called compounds 3) a given compound always contain the same proportion of elements

Early Models of the Atom By the late 1700s, experiments carried out by French chemists Proust, Priestley, and Lavoisier suggested that matter might be made of atoms after all. After very careful experiments with precise measurements, English school teacher John Dalton combined his own ideas with those of the French chemists and proposed the first atomic theory of matter based on experimental results in 1803.

Dalton’s Atomic Theory 1. matter is composed, indivisible particles Atoms Can Be Divided, but only in a nuclear reaction 2. all atoms of a particular element are identical Does Not Account for Isotopes (atoms of the same element but a different mass due to a different number of neutrons)! 3. different elements have different atoms YES! 4. atoms combine in certain whole-number ratios YES! Called the Law of Definite Proportions 5. In a chemical reaction, atoms are merely rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements. Yes, except for nuclear reactions that can change atoms of one element to a different element

Dalton’s Impact People didn’t really believe Dalton’s theory. Scientists wanted better proof For a century after Dalton made his proposal, it remained hypothetical. Many scientists doubted the existence of atoms at all. It was Einstein who observed Brownian motion in 1905 thus proved atoms existed

Law of Constant Composition A given compound always contains the same proportion by mass of the elements of which it is composed. The law of constant composition states that the composition of a substance is always the same, regardless of how the substance was made or where the substance is found. So, whenever we talk about water, we know that there are 2 atoms of hydrogen and 1 atom of oxygen in a molecule of water. As soon as the composition of a molecule changes, then you have a different substance with different properties.

Hennig Brand Wanted to fine the “philospher’s stone” which turned bass metals into gold. Around 1669 he heated residues from boiled-down urine on his furnace until the retort was red hot, where all of a sudden glowing fumes filled it and liquid dripped out, bursting into flames. He could catch the liquid in a jar and cover it, where it solidified and continued to give off a pale-green glow. What he collected was phosphorus, which he named from the Greek for "light-bearing" or "light-bearer."

Carl Schelee (1742-1786) Died at 43 surrounded by toxic chemicals and had a stunned look on his face Devised a way to manufacture phosphorus without urine. Hense why Sweden is still #1 in matches. Discovered Oxygen, chlorine, fluorine, nitrogen and got no credit for it!! Loved Tasting Chemicals… Mercury, hydrocyanic acid

J.J Thompson Late 1890’s, Mr. Thompson used a cathode ray tube to show that atoms of any element can be made to emit tiny negative particles. Discovered Electrons. But they must be balanced by positive particles.

A. The Structure of the Atom The Plum Pudding Model

Ernest Rutherford From New Zealand and got a scholarship to Cambridge and worked under Thompson. In 1910, Rutherford fired ionized helium atoms, or alpha particles, at a sheet of gold foil. To Rutherford’s astonishment, some of the particles bounced back. It was if, he said, he had fired a fifteen inch shell at a sheet of paper and it rebounded on his lap. Explanation: The particles that bounced back were striking something small and dense at the heart of the atom.

Rutherford Rutherford’s Experiment

Rutherford

Discovery of the Neutron In 1935, James Chadwick received the Nobel Prize in Physics for finding neutrons. When Rutherford discovered the proton, he figured that there must be another particle making up the mass of the nucleus. The Curies (of radiation fame) also worked to find the neutron but misread their results and missed the discovery. (they won the Nobel Prize in Chemistry in 1935 so don’t feel so bad.)

Introduction to the Modern Concept of Atomic Structure Ernest Rutherford showed that atoms have internal structure. The nucleus, which is at the center of the atom, contains protons (positively charged) and neutrons (uncharged). Electrons move around the nucleus.

ATOM COMPOSITION The atom is mostly empty space protons and neutrons in the nucleus. the number of electrons is equal to the number of protons. electrons in space around the nucleus. extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water.

ATOMIC COMPOSITION Protons (p+) + electrical charge mass = 1.672623 x 10-24 g relative mass = 1.007 atomic mass units (amu) but we can round to 1 Electrons (e-) negative electrical charge relative mass = 0.0005 amu but we can round to 0 Neutrons (no) no electrical charge mass = 1.009 amu but we can round to 1

If all atoms are composed of these same components, why do different atoms have different properties The answer lies in the number and arrangement of the electrons. The electrons are the parts of atoms that “intermingle” when atoms combine to form molecules. As a result, atoms of different elements, which have different numbers of electrons, show different chemical behavior.

Atomic Number, Z All atoms of the same element have the same number of protons in the nucleus, Z 13 Atomic number Al Atom symbol 26.981 AVERAGE Atomic Mass

Mass Number, A C atom with 6 protons and 6 neutrons is the mass standard = 12 atomic mass units Mass Number (A) = # protons + # neutrons NOT on the periodic table…(it is the AVERAGE atomic mass on the table) A boron atom can have A = 5 p + 5 n = 10 amu

Isotopes Atoms of the same element (same Z) but different mass number (A). Boron-10 (10B) has 5 p and 5 n Boron-11 (11B) has 5 p and 6 n 10B 11B

Figure 3.10: Two isotopes of sodium.

Isotopes & Their Uses Bone scans with radioactive technetium-99.

Isotopes & Their Uses The tritium content of ground water is used to discover the source of the water, for example, in municipal water or the source of the steam from a volcano.

Atomic Symbols Show the name of the element, a hyphen, and the mass number in hyphen notation sodium-23 Show the mass number and atomic number in nuclear symbol form mass number 23 Na atomic number 11

Isotopes? Which of the following represent isotopes of the same element? Which element? 234 X 234 X 235 X 238 X 92 93 92 92

Counting Protons, Neutrons, and Electrons Protons: Atomic Number (from periodic table) Neutrons: Mass Number minus the number of protons (mass number is protons and neutrons because the mass of electrons is negligible) Electrons: If it’s an atom, the protons and electrons must be the SAME so that it is has a net charge of zero (equal numbers of + and -) If it does NOT have an equal number of electrons, it is not an atom, it is an ION. For each negative charge, add an extra electron. For each positive charge, subtract an electron (Don’t add a proton!!! That changes the element!)

Warm up 1/30/2013 – Counting Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12C 13C 14C 6 6 6 #p+ _______ _______ _______ #no _______ _______ _______ #e- _______ _______ _______

Answers 12C 13C 14C 6 6 6 #p+ 6 6 6 #no 6 7 8 #e- 6 6 6

Learning Check An atom has 14 protons and 20 neutrons. A. Its atomic number is 1) 14 2) 16 3) 34 B. Its mass number is C. The element is 1) Si 2) Ca 3) Se D. Another isotope of this element is 1) 34X 2) 34X 3) 36X 16 14 14