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Elements & Atoms with Mr. Khatter Elements The purest form of something – so pure that there’s NOTHING you can do to it to separate it into something else. Left to right: pure forms of the metals Cobalt, Iron, and Nickel • An _____ is the smallest particle of an element that has the chemical properties of the element. Copper atoms on silica surface. The Atom An atom consists of a • nucleus –(of protons and neutrons) • electrons in space about the nucleus. Electron cloud Nucleus Atoms All matter is composed of small, fast moving particles called atoms. These atoms can join together to form molecules. This theory is really thousands of individual theories that provide evidence for the whole theory. Atoms Since the atom is too small to be seen even with the most powerful microscopes, scientists rely upon Believe it or not this is a microscope. Even with the models to help us to world’s best microscopes we cannot clearly see the understand the structure or behavior of the atom. atom. Scientific Models Scientists create models to help them to visualize complex properties, structures or behaviors. Since the atom is so small, scientists must gather indirect evidence to develop their models. This is a model of a very complex molecule made of many different kinds of atoms. Each colored ball represents an atom of a different element. Is this really an Atom? This model (left) represents the most modern version of the atom. (Artist drawing) 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 Atomic Number All atoms of the same element have the same number of protons in the nucleus 13 Atomic number Al Atom symbol 26.981 AVERAGE Atomic Mass Mass Number • C atom with 6 protons and 6 neutrons is the mass standard • = 12 atomic mass units • Mass Number = # protons + # neutrons • NOT on the periodic table…(it is the AVERAGE atomic mass on the table) • A boron atom can have 5 p + 5 n = 10 amu Isotopes • Atoms of the same element but different mass number. • Boron-10 (10B) has 5 p and 5 n • Boron-11 (11B) has 5 p and 6 n 11B 10B 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 in 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 pairs represent isotopes of the same element? 234 234 235 238 X X X X 92 93 92 92 Learning Check – 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 1) 14 2) 16 3) 34 C. Another isotope of this element is 1) 34X 2) 34X 3) 36X 16 14 14 Elements & Atoms with Mr. Khatter… The journey continues AVERAGE 11B ATOMIC 10B MASS • The atomic mass an atom is usually listed underneath the atom’s alphabetical symbol on the periodic table. • The atomic mass is an average of the masses of the atom in its various forms (isotopes). AVERAGE 11B ATOMIC 10B MASS • Boron exists in its balanced form with 5 protons and 5 neutrons only 20% of the time (as far as we’ve found it in nature so far). • In other words, 20% of the time we have found Boron, it has had an atomic mass of 10. • The other 80% of the time it has an atomic mass of 11, meaning that it has 5 protons and 6 neutrons. AVERAGE 11B ATOMIC 10B MASS • By knowing that Boron exists with an atomic mass of 10 (5p + 5n) 20% of the time and with an atomic mass of 11 (6p + 5n) 80% of the time, scientists created the following formula to find Boron’s average atomic mass of 10.811. (20% x 10) + (80% x 11) AVERAGE ATOMIC MASS 7.5% of the time, Lithium exists as Lithium-6, with 3 protons and 3 neutrons. The other 92.5% of the time, it exists as Lithium-7, with 3 protons and 4 neutrons. 1.) Write out the equation scientists use to find its average Atomic Mass. 28Si = 92.23%, 29Si = AVERAGE ATOMIC 4.67%, 30Si = 3.10% MASS Avg. Atomic mass of Si = ______________ 92.23% of the time, Silicon exists as Silicon-28, with 14 protons and 14 neutrons. 4.67% of the time, Silicon exists as Silicon-29, with 14 protons and 15 neutrons. The other 3.1% of the time, it exists as Silicon-30, with 14 protons and 16 neutrons. 2.) Write out the equation scientists use to find its average Atomic Mass. Quick Check Complete the sentences below. 3.) Atoms always have an equal number of ____________ and ____________, each of which is equal to the atom’s ____________ number. 4.) Atoms that have unequal numbers of neutrally charged ____________ and positively charged protons are called ____________. Quick Check Complete the sentences below. 3.) Atoms always have an equal number of protons and electrons, each of which is equal to the atom’s atomic number. 4.) Atoms that have unequal numbers of neutrally charged neutrons and positively charged protons are called isotopes. Electron Organization The electrons in an atom are organized in energy levels. The levels farther from the nucleus contain electrons that have more energy than levels closer to the nucleus. Electron Organization Electron Organization Electron Organization Electron Organization Electron Organization 2 electrons – 1st level 8 electrons – 2nd level 8 electrons – 3rd level 5.) Sulfur has an atomic number of 16. How many atoms does it have in each level? Draw a model to answer. 2 – 1st level 8 – 2nd level 6 – 3rd level Electron Organization 2 electrons – 1st level 8 electrons – 2nd level 8 electrons – 3rd level 6.) Magnesium has an atomic number of 12. How many atoms does it have in each level? Draw a model to answer. 2 – 1st level 8 – 2nd level 2 – 3rd level Look at the outermost energy level of each of these atoms. The electrons in an atom’s outermost energy level are called that atom’s valence electrons. Complete these sentences: 7.) Sulfur has _____ valence electrons. 8.) Magnesium has _____ valence electrons. Complete these sentences: 7.) Sulfur has 6 valence electrons. 8.) Magnesium has 2 valence electrons.
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