1 / 165

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

spoon
Download Presentation

Chapter 6 The Structure of Matter

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related