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Chapter 6 The Structure of Matter

Chapter 6 The Structure of Matter. Compounds and Molecules. Forces that hold atoms or ions together in a compound are called chemical bonds Chemical structure is the way the compound’s atoms are bonded to make the compound Bond length: distance between the nuclei of two bonded atoms

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Chapter 6 The Structure of Matter

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  1. Chapter 6The Structure of Matter

  2. Compounds and Molecules • Forces that hold atoms or ions together in a compound are called chemical bonds • Chemical structure is the way the compound’s atoms are bonded to make the compound • Bond length: distance between the nuclei of two bonded atoms • Bond angle: angle formed by the bonds

  3. Compounds and Molecules • The chemical structure of a compound determines the properties of that compound • Compounds with a network structure • Strong solids with very high melting/boiling points • Quartz • Compounds with network of bonded ions • High melting/boiling points • Salt • Compounds of molecules • Bonds weaker

  4. Atoms • The figure TO THE RIGHT shows the subatomic particles in a helium atom • The subatomic particles that make up atoms are protons, neutrons, and electrons • Protons and neutrons have about the same mass • However, protons are positively charged particles (+) and neutrons carry no charge • Their name is a reminder that they are neutral particles • Strong forces bind protons and neutrons together to form the nucleus, which is at the center of the atom

  5. Atoms

  6. Atoms • Helium atoms contain protons, neutrons, and electrons: • The positively charged protons and uncharged neutrons are bound together in the dense nucleus, while the negatively charged electrons move in the space around the nucleus

  7. Atoms • The electron is a negatively charged particle (−) with 1/1840 the mass of a proton • Electrons are in constant motion in the space surrounding the nucleus • They are attracted to the positively charged nucleus but remain outside the nucleus because of the energy of their motion • Because atoms have equal numbers of electrons and protons, and because these subatomic particles have equal but opposite charges, atoms are neutralbefore they react!!!!!!

  8. Elements • A chemical element is a pure substance that consists entirely of one type of atom • More than 100 elements are known, but only about two dozen are commonly found in living organisms • Elements are represented by a one- or two-letter symbol • Example: • C stands for carbon • H for hydrogen • Na for sodium • The number of protons in an atom of an element is the element's atomic number • Carbon's atomic number is 6, meaning that each atom of carbon has six protons and, consequently, six electrons

  9. ATOM • IS THE FUNDAMENTAL UNIT OF MATTER • COMPOSED OF SUBATOMIC PARTICLES • ATOMIC NUCLEUS • PROTON • NEUTRON • ELECTRONS:ORBIT (OUTSIDE) THE NUCLEUS 

  10. ATOMIC NUMBER — THE NUMBER OF PROTONS IN THE NUCLEUS OF THE ATOM. • BEFORE AN ATOM REACTS THE NUMBER OF PROTONS AND ELECTRONS ARE EQUAL 

  11. MASS NUMBER (ATOMIC MASS) — IS THE SUM OF THE PROTONS AND NEUTRONS IN THE NUCLEUS OF THE ATOM. • amu = .000,000,000,000,000,000,000,001,67 g • Electron mass is so small (negligible) that when calculating MASS NUMBER of an atom the mass of the electron is considered zero ( 0).

  12. LOCATION MASS CHARGE • ( in amu) • _____________________________________ PROTON nucleus 1 +1 • _____________________________________ • NEUTRON nucleus 1 0 • _____________________________________ • ELECTRON outside 1/2000 -1 • nucleus • _____________________________________

  13. LOCATION MASS CHARGE • ( in amu) • _____________________________________ PROTON nucleus 1 +1 • _____________________________________ • NEUTRON nucleus 1 0 • _____________________________________ • ELECTRON outside 1/2000 -1 • nucleus • _____________________________________

  14. Isotopes • Atoms of an element can have different numbers of neutrons • Example: • Some atoms of carbon have six neutrons, some have seven, and a few have eight • Atoms of the same element that differ in the number of neutrons they contain are known as isotopes • The sum of the protons and neutrons in the nucleus of an atom is called its mass number • Isotopes are identified by their mass numbers. • The figure at right shows the subatomic composition of carbon-12, carbon-13, and carbon-14 atoms • The weighted average of the masses of an element's isotopes is called its atomic mass • “Weighted” means that the abundance of each isotope in nature is considered when the average is calculated • Because they have the same number of electrons, all isotopes of an element have the same chemical properties

  15. Isotopes of Carbon • Because they have the same number of electrons, these isotopes of carbon have the same chemical properties • The difference among the isotopes is the number of neutrons in their nuclei

  16. Isotopes of Carbon

  17. Radioactive Isotopes  • Some isotopes are radioactive, meaning that their nuclei are unstable and break down at a constant rate over time: • The radiation these isotopes give off can be dangerous, but radioactive isotopes have a number of important scientific and practical uses: • Geologists can determine the ages of rocks and fossils by analyzing the isotopes found in them • Radiation from certain isotopes can be used to treat cancer and to kill bacteria that cause food to spoil • Radioactive isotopes can also be used as labels or “tracers” to follow the movements of substances within organisms

  18. Chemical Compounds • In nature, most elements are found combined with other elements in compounds • A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions • Scientists show the composition of compounds by a kind of shorthand known as a chemical formula: • Water, which contains two atoms of hydrogen for each atom of oxygen, has the chemical formula H2O • The formula for table salt, NaCl, indicates that the elements from which table salt forms—sodium and chlorine—combine in a 1 : 1 ratio

  19. Chemical Compounds • The physical and chemical properties of a compound are usually very different from those of the elements from which it is formed: • Example: • Hydrogen and oxygen, which are gases at room temperature, can combine explosively and form liquid water • Sodium is a silver-colored metal that is soft enough to cut with a knife • It reacts explosively with cold water • Chlorine is very reactive, too • It is a poisonous, greenish gas that was used to kill many soldiers in World War I. • Sodium and chlorine combine to form sodium chloride (NaCl), or table salt • Sodium chloride is a white solid that dissolves easily in water. As you know, sodium chloride is not poisonous • In fact, it is essential for the survival of most living things

  20. Chemical Compounds • Empirical formula: is the simplest formula for a compound • NaCl : • No number is written to the left of Na • Therefore, one is understood • No subscripts are written to the right of Na and Cl • Therefore, one is understood • 2H2O : • How many water molecules? • How many atoms of H? • How many atoms of O?

  21. Radicals (Polyatomic) • The formulas for some compounds contain groups of two or more atoms that act as if they are one atom • OH : hydroxide • SO4 : sulfate • ClO3 : chlorate • NO3 : nitrate • CO3 : carbonate • PO4 : phosphate

  22. Compounds that contain Radicals (Polyatomic) • When a compound contains more than one radical, the radical is written in parentheses • A subscript outside the parentheses tells you how many units of the radical are in one molecule of the compound • Al(OH)3 : aluminum hydroxide • Ba(NO3)2 : barium nitrate

  23. Bonding Patterns • Ionic bond: transfer of electron • Covalent bond: sharing of electron

  24. Chemical Bonds • The atoms in compounds are held together by chemical bonds • Much of chemistry is devoted to understanding how and when chemical bonds form • Bond formation involves the electrons that surround each atomic nucleus: • The electrons that are available to form bonds are called valence electrons • The main types of chemical bonds are ionic bonds and covalent bonds

  25. Ionic Bonds  • An ionic bond is formed when one or more electrons are transferred from one atom to another • Recall that atoms are electrically neutral because they have equal numbers of protons and electrons • Electrically stable BUT chemically unstable • An atom that loses electrons has a positive charge • An atom that gains electrons has a negative charge • These positively and negatively charged atoms are known as ions

  26. ATOMIC NUMBER — THE NUMBER OF PROTONS IN THE NUCLEUS OF THE ATOM • BEFORE AN ATOM REACTS THE NUMBER OF PROTONS AND ELECTRONS ARE EQUAL 

  27. ELECTRONS • Do not move about an atom in definite orbits • Only the probability of finding an electron at a particular place in an atom can be determined • Each electron seems to be locked into a certain area in the electron cloud

  28. Modern Atomic Theory • Electrons are arranged in energy levels • An energy level represents the most likely location in the electron cloud in which an electron can be found

  29. MODERN ATOMIC THEORY • Electrons with the lowest energy are found in the energy level closest to the nucleus • Electrons with the highest energy are found in the energy levels farther from the nucleus • Each energy level can hold only a maximum number of electrons

  30. MODERN ATOMIC THEORY • First energy level—maximum of 2 electrons • Second energy level— maximum of 8 electrons • Third energy level—maximum of 18 electrons (three sublevels of 2/8/8)

  31. Chemical activity—depends on the arrangement of electrons in the outermost energy level

  32. FORCES WITHIN THE ATOM • Electromagnetic—negative charged electrons are attracted to the positive charged protons  • Strong Force—prevents the positively charged protons from repelling each other • keeps protons together  • Weak Force—responsible for radioactive decay • neutron changes into a proton and an electron  • Gravity: force of attraction that depends on the mass of two objects and the distance between them

  33. ATOMS AND BONDING • Before an atom reacts it is electrically neutral (same number of protons and electrons) — electrically stable

  34. ATOMS AND BONDING: • However the atom might not be chemically stable: • Chemical stability depends on the valence electrons (outermost energy level) • 1/2/3 electrons — will lose electrons • 5/6/7 electrons — will gain electrons • after losing/gaining electrons the atom will be chemically stable but now will become electrically unstable

  35. ATOMS AND BONDING: • lose 1 electron +1 • lose 2 electrons +2 • lose 3 electrons +3 • gain 3 electrons -3 • gain 2 electrons -2 • gain 1 electron -1 • When the outermost energy level (valence electrons) is filled, the atom is chemically stable

  36. IONIC BONDS—involves the transfer of electrons • One atom gains electrons and the other atom loses electrons resulting in filled outer energy levels • Ions are formed (charged atom or group of atoms — polyatomic)

  37. Ionic Bonds • The figure above shows how ionic bonds form between sodium and chlorine in table salt • A sodium atom easily loses its one valence electron and becomes a sodium ion (Na+) • A chlorine atom easily gains an electron and becomes a chloride ion (Cl−)

  38. Ionic Bonds

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