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Chapter 2

Chapter 2. In 1808 an English scientist John Dalton, formulated a precise definition of the of atoms:. 2.2 The Structure of the Atom After Dalton a series of investigations led to the discovery of three smaller particles: electrons, protons and neutrons. Atomic components:.

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Chapter 2

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  1. Chapter 2

  2. In 1808 an English scientist John Dalton, formulated a precise definition of the of atoms:

  3. 2.2 The Structure of the AtomAfter Dalton a series of investigations led to the discovery of three smaller particles: electrons, protons and neutrons.

  4. Atomic components:

  5. All atoms can be identified by the number of protons and neutrons they contain. The atomic number (Z) is the number of protons in the nucleus of each atom of an element. In a neutral atom the number of protons is equal to the number of electrons, so the atomic number also indicates the number of electrons present in the atom.

  6. A A X X Mass Number Mass Number Element Symbol Element Symbol Z Z Atomic Number Atomic Number 2 1 3 2 1 3 H (T) H (D) H (D) H (T) H H 1 1 1 1 1 1 235 238 U U 92 92 Atomic number, Mass number and Isotopes Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopesare atoms of the same element (X) with different numbers of neutrons in their nuclei

  7. The Isotopes of Hydrogen

  8. 23 24 Na Na 11 11 How many protons, neutrons, and electrons are in How many protons, neutrons, and electrons are in ? ? 11 protons, 13 (24 - 11) neutrons, 11 electrons 11 protons, 12 (23-11) neutrons, 11 electrons

  9. IonsWhen a neutral atom accept or lose one electron or more it is named an ion. If it lose electrons it is called Cation ( ion with a –ve charge. And named Anion if it accept electrons.Examples page 36 – 40 Arabic book

  10. 2.4 The Periodic TableThe periodic table, a chart in which elements having similar chemical and physical properties are grouped together. Figure 2.10 shows the modern periodic table in which the elements are arranged by atomic number (shown above the element symbol) in horizontal rows called periods and in vertical columns known as groups or families, according to similarities in their chemical properties.The elements can be divided into three categories—metals, nonmetals, and metalloids. A metal is a good conductor of heat and electricity while a nonmetal is usually a poor conductor of heat and electricity.A metalloid has properties that are intermediate between those of metals and nonmetals. Figure 2.10 shows that the majority of known elements are metals; only 17 elements are nonmetals, and 8 elements are metalloids. From left to right across any period, the physical and chemical properties of the elements change gradually from metallic to nonmetallic.The periodic table correlates the properties of the elements in a systematic way and helps us to make predictions about chemical behavior. We will take a closer look at this keystone of chemistry in Chapter 8.

  11. Noble Gas Halogen Alkali Earth Metal Period Alkali Metal Group The Modern Periodic Table

  12. diatomic elements 2.5 Molecules and Ions A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical forces H2 H2O NH3 CH4 A diatomic molecule contains only two atoms H2, N2, O2, Cl2, HCl, CO A polyatomic molecule contains more than two atoms O3, H2O, NH3, CH4

  13. 11 protons 11 electrons 11 protons 10 electrons Na+ Na 17 protons 18 electrons 17 protons 17 electrons Cl- Cl An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion.

  14. A monatomic ion contains only one atom K+, F-, Mg2+, O2-, Al3+, N3- A polyatomic ion contains more than one atom OH-, CN-, NH4+, NO3-

  15. How many protons and electrons are in ? 2+ 56 How many protons and electrons are in ? Fe 26 14 3- N 7 7protons, 10 (17+3) electrons 26 protons, 24 (26-2) electrons

  16. 2.6 Chemical FormulasChemists use chemical formulas to express the composition of molecules and ionic compounds in terms of chemical symbols. By composition we mean not only the elements present but also the ratios in which the atoms are combined. Here we are concerned with two types of formulas: 1- molecular formulas and 2- empirical formulas.Molecular FormulasA molecular formula shows the exact number of atoms of each element in the .smallest unit of a substanceThus, H2 is the molecular formula for hydrogen,O2 is oxygen, O3 is ozone, and H2O is water. Molecular Models: ball-and-stick models and space-filling models ( Figure 2.12) The structural formula:which shows how atoms are bonded to one another in a molecule.

  17. Formulas and Models

  18. molecular empirical H2O A molecular formula shows the exact number of atoms of each element in the smallest unit of a substance An empirical formula shows the simplest whole-number ratio of the atoms in a substance H2O CH2O C6H12O6 O3 O N2H4 NH2

  19. ionic compounds consist of a combination of cations and an anions • The formula is usually the same as the empirical formula • The sum of the charges on the cation(s) and anion(s) in each formula unit must equal zero The ionic compound NaCl

  20. The most reactive metals (green) and the most reactive nonmetals (blue) combine to form ionic compounds.

  21. 1 x 2+ = 2+ 2 x 3+ = 6+ 1 x 2+ = 2+ 3 x 2- = 6- 2 x 1- = 2- 1 x 2- = 2- Formula of Ionic Compounds Al2O3 Al3+ O2- MgCl2 Ca2+ Br- Na2CO3 Na+ CO32-

  22. An acidcan be defined as a substance that yields hydrogen ions (H+) when dissolved in water. • For example: HCl gas and HCl in water • Pure substance, hydrogen chloride • Dissolved in water (H3O+ and Cl−), • hydrochloric acid

  23. nitric acid HNO3 carbonic acid H2CO3 H3PO4 phosphoric acid An oxoacid is an acid that contains hydrogen, oxygen, and another element.

  24. sodium hydroxide NaOH potassium hydroxide KOH Ba(OH)2 barium hydroxide A base can be defined as a substance that yields hydroxide ions (OH-) when dissolved in water.

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