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The Structure of Matter: Atoms, Nucleus, and Energy Levels

This unit provides an overview of the structure of matter, including atoms, the nucleus, and energy levels. Topics covered include the periodic table, Bohr diagrams, ionic compounds, and molecular compounds. Discover how elements form compounds and the difference between natural and synthetic products.

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The Structure of Matter: Atoms, Nucleus, and Energy Levels

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  1. Science 20F Unit 1 – Chemicals in Action Developed by Trevor Boehm Hutterian Interactive TV System Prairie Rose School Division

  2. Unit 1 Overview • The Structure of Matter • The Periodic Table (Text Topic 5.5) • Bohr Diagrams • How Elements Form Compounds (Text Topic 5.6) • Ionic Charges and Chemical Families (Text Topic 5.7) • Ionic Compounds (Text Topic 5.8) • Polyatomic Ions in Ionic Compounds (Text Topic 5.9) • Molecular Compounds (Text Topic 5.11) • Natural vs. Synthetic Products (Text Topic 5.13)

  3. What’s (The) Matter? • Matter is anything which has mass and takes up space. • Mass = weight (not exactly, but close enough for our purposes). • All matter is composed of atoms. • There are three states matter can exist in: solid, liquid, and gas.

  4. The Atom • An atom is the smallest particle of an element that has the properties of that element. • All matter is made up of atoms. • There are 113 (roughly) different elements known to exist. • Examples of elements you know and love: • oxygen • helium • calcium • iron

  5. Electrons Nucleus Contains Protons and Neutrons Atomic Structure • Atoms are composed of three types of particles: • Protons are positively charged, are heavy, and are found in the nucleus of an atom. • Neutrons have no charge (neutral), and heavy, and are found in the nucleus of an atom. • Electrons are negatively charged, are very light, and are found orbiting the nucleus of an atom.

  6. NUCLEUS The Nucleus of an Atom • In the nucleus of an atom, we have protons and neutrons. • Most of the mass of an atom is in its nucleus – both protons and neutrons are heavy. • In normal chemistry, the nucleus of an atom doesn’t change. • There is a type of chemistry where the nucleus does change, maybe you’ve heard of it…? • We won’t be dealing with nuclear chemistry in this course.

  7. Electrons Energy levels, shells, or orbitals (all mean the same thing) Electrons in Orbit • Electrons are very light (almost no mass) and are found orbiting the nucleus of an atom. • They are held in orbit by the attraction between the positive protons in the nucleus and the negative charge of the electrons. • Electrons orbit the nucleus in “shells” or “energy levels”. • The really important energy level for chemistry is the outermost one. • All chemical reactions involve electrons.

  8. The Periodic Table • The periodic table lists all the known elements (about 113 of them) in an organized way. • Elements on the period table are arranged in order from lowest atomic number to highest atomic number. • The periodic table has 7 rows (periods) and 18 columns (groups).

  9. The Periodic Table

  10. Information about Elements • The periodic table gives you a lot of information about each element. • The most important details listed for an element are: • Symbol (doesn’t always match English name) • Name • Atomic number • Atomic mass Atomic number 4 Be Symbol 9.01218 Atomic mass Beryllium Element Name

  11. Atomic Number • The atomic number of an element is the number of protons in the nucleus of an atom of that element. • It is the number of protons that determines what element an atom is. • All atoms of an element will have the same atomic number and the same number of protons.

  12. Atomic Weight / Mass • Sometimes called atomic mass, sometimes called atomic weight, it means the same thing. • Atomic mass is the number of protons plus the number of neutrons in an atom’s nucleus. • Sometimes there is a decimal part – just ignore it and round off to the nearest whole number. The decimal does mean something, but we don’t need to worry about it.

  13. Figuring Out Protons, Neutrons, and Electrons • The information on the periodic table lets us figure out the number of protons, neutrons, and electrons an element has. • The number of protons is the same as the atomic number. • Protons = Atomic Number • The number of neutrons is the atomic mass (rounded) minus the number of protons. • Neutrons = Atomic Mass – Protons • The number of electrons is the same as the number of protons. • Electrons = Protons

  14. Groups • The columns (vertical - up and down) on the periodic table are called groups. • Groups are also called chemical families. • Elements in the same group have similar chemical properties. • The elements in a group have the same number of electrons in their outermost electron shell. • Groups are labeled with roman numerals (IA, IIA, etc.) • We will be studying the chemical properties of the main chemical families in this unit. Groups (up and down)

  15. Periods • The rows (horizontal - across) on the periodic table are called periods. • These are numbered using normal digits (1, 2, 3…). • The period number tells us what the outermost electron shell of an element is. So an element in the third period (Magnesium, for example) would have three electron shells. • There are 7 rows, so 7 periods. Periods (across)

  16. Ways of Classifying Elements • Elements can be grouped in several ways: • Metals, nonmetals, and metalloids. • Representative elements, transition elements, and inner transition elements. • Chemical families. • Let’s take a look at each, and see how it is shown on the periodic table.

  17. Metals, Nonmetals,and Metalloids • In the textbook (and on the next slide)… • Metals are green. • Nonmetals are orange or blue. • Metalloids are purple.

  18. Metals, Nonmetals,and Metalloids Metals Nonmetals Metalloids Noble gases (nonmetals)

  19. Representative, Transition, and Inner Transition Elements • Representative elements are the ones with a group number that has an A (IA – VIIIA). • Transition elements are the ones with a group number that has a B (IIIB-VIIIB, IB and IIB). • Inner transition elements are the two rows at the bottom of the periodic table (the Lanthanides, atomic number 57-70, and the Actinides, atomic number 89-102).

  20. Representative, Transition, and Inner Transition Elements Representative Elements Transition Elements Inner Transition Elements

  21. Chemical Families • These include: • The Alkali Metals (Group IA) • The Alkaline Earth Metals (Group IIA) • The Halogens (Group VIIA) • The Noble Gases (Group VIIIA) • Note that Hydrogen is unique and has its own chemical family all by itself.

  22. Chemical Families The Alkali Metals (Group IA) The Alkaline Earth Metals (Group IIA) The Halogens (Group VIIA) The Noble Gases (Group VIIIA)

  23. Bohr Models • A Bohr model is a way of drawing what an atom is made of. It shows the protons, neutrons, and electrons in an atom. • Atoms don’t really look like their Bohr models. But we can’t actually see what’s inside an atom – it’s microscopic. • Bohr models will be very useful in figuring out how elements combine to form compounds. • We’re going to look at a sample Bohr model. To keep things simple, let’s look at Helium.

  24. How to Draw a Bohr ModelStep 1 – The Nucleus • First of all, draw a circle. The circle should be big enough to write two short lines inside.

  25. How to Draw a Bohr ModelStep 1 – The Nucleus • Now we need to figure out how many protons and neutrons Helium has: • Protons = Atomic # • Protons = 2 • Neutrons = Atomic Mass – Protons • Neutrons = 4 – 2 = 2 • So Helium has 2 protons and 2 neutrons in its nucleus. Go ahead and write that in the circle. Use a + for protons and an N for neutrons. 2 + 2 N

  26. How to Draw a Bohr ModelStep 2 – The Electrons • Next we need to know how many electrons Helium has: • Electrons = Protons • Electrons = 2 • So Helium has 2 electrons. • The electrons are orbiting in a circle outside the nucleus. So draw another circle, then put two electrons on opposite ends of that circle. Use a - for the electrons. 2 + 2 N - -

  27. How to Draw a Bohr ModelStep 3 – Label It • Last thing to do is label this Bohr model with the symbol for the element Helium. • Pretty simple, huh? Well, it does get more complicated. He 2 + 2 N - -

  28. Electron Energy Levels • Different energy levels hold different numbers of electrons. • An energy level must be completely full before electrons will be placed into the next energy level. • When drawing a Bohr model, start by drawing the orbital closest to the atom and then working your way out as the orbitals are filled.

  29. How Many Electronsin Each Orbital?

  30. The Simplified Version • For the first 20 elements (up to Calcium): • The K orbital will hold 2 electrons. • The L orbital will hold 8 electrons. • The M orbital will hold 8 electrons. • The N orbital will hold 2 electrons. • So just remember… 2 8 8 2. • Things get more complicated after the first 20 elements. Ask me if you really want to know… but it can get confusing.

  31. A More Complex Bohr ModelStep 1 – The Nucleus • For this example, let’s do Oxygen (symbol O). • Circle with protons and neutrons inside. 8 + 8 N

  32. A More Complex Bohr ModelStep 2 – The Electrons • Next we need to draw the electrons. Oxygen has 8 of then. • The K shell can hold 2 electrons. • The K shell is now full. 8 + 8 N - -

  33. A More Complex Bohr ModelStep 2 – The Electrons • We need to put the rest of the electrons in the L shell. • The L shell can hold 8 electrons. • We only have 6 more to draw. Let’s draw them, leaving room for the 2 more that could fit in the L shell but aren’t there. O - - 8 + 8 N Space for 2 more electrons (L shell can hold 8) - - - - - -

  34. Chemical Reactivityof Elements • Chemical reactivity means how likely an element is to combine with other elements. • The chemical reactivity of an element is determined by the number of electrons in its outermost shell. • This is called the number of valence electrons. • For the representative elements only (groups with an A), the group number is the number of valence electrons. • All atoms want to be chemically stable – to have a full outer shell. • The noble gases (Group VIIIA) already have a full outer shell, this means that they are chemically inert and will not react or form compounds. • The rest of the elements will need to gain, lose, or share electrons to get a complete outer shell.

  35. The Formation of Compounds • In order to get a complete outer shell, atoms form compounds. • A compound is made of two or more atoms of different types. • There are two types of compounds: • Ionic compounds • Molecular compounds

  36. Ions • Ionic compounds are formed when one atom loses electron(s) and another gains electron(s). • Remember that in a neutral atom, the number of electrons is the same as the number of protons. Neutral means no charge. • Ions are atoms which have either gained or lost electrons. An ion is a charged atom. • When an atom loses one or more electrons, it will have a positive charge (more protons than electrons). • When an atom gains one or more electrons, it will have a negative charge (more electrons than protons). • Charge can always be figured out by the formula: • Charge = # of protons – # of electrons

  37. Ionic Compounds • An ionic compound is made up of one or more positive ions and one or more negative ions. • The compound is held together by the attractive force between the positive ion(s) and the negative ion(s). • Remember the old saying “opposites attract”? In chemistry, it’s true. • The overall charge of an ionic compound will always be 0. • Ionic compounds are electrolytes, which means they will conduct electricity when dissolved in water.

  38. Metals, Nonmetals, Ions, and Mary’s Lamb • Metals combine with non-metals to form ionic compounds. • Metal atomslose electrons to form positive ions (cations). • Nonmetal atomsgain electrons to form negative ions (anions). Mary’s Lamb Parties Nightly Getting Nowhere.

  39. An Example of anIonic Compound • We need a metal… let’s take Sodium (symbol Na). • And we weed a non-metal. Let’s take Chlorine (symbol Cl). • Sodium has a valence of 1, and it’s a metal. In order to get a complete outer shell, it needs to lose its lonely electron. • Chlorine has a valence of 7, and it’s a non-metal. In order to get a complete outer shell, it needs to find an atom to give it one more electron. • Sodium and Chlorine are, chemically speaking, an “ideal couple”.

  40. The Wedding • Sodium, do you take this Chlorine to be your lawfully wedded ion? • And Chlorine, do you take this sodium to be your lawfully wedded ion? • You may exchange the electron. • I now pronounce you “Sodium Chloride”.

  41. Here’s What Happened • Sodium lost an electron. The Sodium atom became a Sodium ion with a + charge. It now has a complete outer shell. • Chlorine gained an electron (from the Sodium). The Chlorine atom became a Chlorine ion with a - charge. It now has a complete outer shell. • The attractive force between the Sodium + ion and the Chlorine - ion pulled the two ions together to form an ionic compound. • The overall charge of the ionic compound is still 0.

  42. A Hint for WorkingOut Ionic Compounds • Look at how many electrons the atom has in its outer shell. • Figure out how many it would need to gain to completely fill its outer shell. • Also figure out how many it would need to lose in order to totally empty the current outer shell. • Whichever is easier, that’s what the atom is going to do. • Atoms are lazy. They don’t do more work than needed.

  43. Naming Binary Compounds • A binary compound is one that only has two elements. • “bi” means two (think “bicycle”, two wheels). • When naming a binary compound, the name of the second element has the ending “-ide”. • So… in the case of the ionic compound formed when Sodium and Chlorine tied the knot… • Sodium Chloride.

  44. Writing the Chemical Formula of an Ionic Compound • Instead of saying “Sodium”, “Chlorine”, and “Sodium Chloride”, we can use their chemical symbols instead. • The chemical formula of Sodium Chloride is NaCl. • The metal ion always comes first in the formula. • By the way… has anyone figured out what NaCl is yet?

  45. Another Exampleof a Binary Compound • Let’s take Calcium (Ca)… atomic number 20. • Valence of 2. • Metal. • Will need to lose 2 electrons. • And Chlorine (Cl)… atomic number 17. • Valence of 7. • Will need to gain 1 electron. • How many atoms of Chlorine will be needed to take the 2 electrons that Calcium must lose? • That’s right, 2.

  46. Another Exampleof a Binary Compound • So we have one Calcium atom, which will lose 2 electrons, and become a Calcium ion with a charge of 2+. • And we have two Chlorine atoms, which will each gain 1 electron, and become Chlorine ions with charges of 1-. • Our ionic compound will have 1 Calcium ion and 2 Chlorine ions. • How do we write this formula?

  47. Subscripts • When we have more than one atom in a chemical formula, we indicate this using a subscript. • A subscript is a small number written after and just below the chemical symbol. • So to write “two Chlorine atoms” in a chemical formula, we would write “Cl2” • We don’t write a subscript if there is only one atom. The 1 is assumed. • We name our compound Calcium Chloride… • And we write its formula CaCl2.

  48. Superscripts • While on the topic of writing numbers after a chemical symbol… • A superscript a small number written above and right after the symbol for an ion. • A superscript is used to indicate charge of the ion. • So for example, if we wanted to write the formula for a Calcium ion, we would write Ca2+. • This sets the Calcium ion, which has lost two electrons, apart from the Calcium atom, which has no charge and still has all its electrons.

  49. The Criss-Cross Rule • There is an easy way to figure out how many atoms of each element will be needed for an ionic compound. • We call this the “criss-cross rule”. It will make sense in a few moments.

  50. The Criss-Cross RuleStep 1 – Write the Symbols • Write the symbols for the metal and the nonmetal. • Remember, metal comes first. Ca Cl

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