Elements, Atoms

1
Elements, Atoms IonsChapter 4(except 4.3,
4.5)
2
4.1 Elements

• Substances that cannot be decomposed into simpler
  substances by chemical or physical means.
• Each element consists of atoms having the same
  atomic number.
• Over 112 known 88 are found in nature, rest are
  man-made (per your text).
• Abundance is the percentage found in nature
• Oxygen is most abundant element (by mass) in the
  crust of the earth and in the human body (Tables
  4.1, 4.2).
• However, iron is the most abundant element (by
  mass) throughout the entire earth.

3
4.4 Formulas Describe Compounds

• 4.2 Symbols for Elements
• Each element has a unique symbol
• The symbol of an element may be one letter or two
• If two letters, the second is lower case

• A compound is a distinct substance composed of
  atoms of two or more elements.
• Compounds always contain the same relative
  numbers of atoms of each element
• Compounds always contain the same relative masses
  of each element

4

• A formula describes a compound by indicating the
  number and type of each atom present in the
  simplest unit of the compound
• Examples
• Rules for writing formulas (pg 90)
• each element is represented by its letter symbol
• the number of atoms of each element is written to
  the right of the element as a subscript
• When only one atom of a type is given, the
  subscript 1 is not written
• polyatomic groups are placed in parentheses (if
  more than one)
• Examples

5
4.6 The Modern Concept of Atomic Structure

• Atoms are the fundamental units of which elements
  are composed. The smallest unit of matter that
  retains all properties of an element.
• Atoms are composed of three main parts protons,
  neutrons and electrons.
• The nucleus contains protons () and neutrons
  (0).
• The electrons (-) are arranged in energy levels
  (orbitals) outside the nucleus.
• In a neutral atom,
• protons electrons

6

• The number of protons in the nucleus is the
  atomic number (Z).
• The number of protons plus neutrons in the
  nucleus is the mass number (A).
• Electrons of different atoms interact to form
  bonds. Therefore, the number of electrons an
  atom possesses determines its chemical behavior.
  
• Size of atom (see fig 4.9)
• Diameter of nucleus 10-13 cm
• Diameter of overall atom 10-8 cm
• Diameter of an atom is about 100,000 times the
  diameter of the nucleus!
• Atoms are mostly empty space!

7

• Masses of parts of an atom
• Electron 1 (relative mass)
• Proton 1836
• Neutron 1839
• -- most of the mass of an atom is located in the
  nucleus the mass of the electrons is
  insignificant
• In summary
• Atoms are very small, although the overall
  diameter of an atom is very large compared to the
  diameter of the atoms nucleus.
• Almost all the mass is located in the very tiny
  nucleus, making it very dense.

8
4.7 Isotopes

• All atoms of an element have the same number of
  protons
• Atoms of an element with different numbers of
  neutrons are called isotopes
• All isotopes of an element are chemically
  identical and behave the same in chemical
  reactions
• Isotopes of an element have different masses
• Isotopes are identified by their mass numbers
• mass number protons neutrons
• See examples on page 96

9
4.8 Introduction to the Periodic Table

• See class handout for this section.

9
10
4.9 Natural States of the Elements

• Elements are usually not found in pure form in
  nature (on earth).
• Matter around us consists mostly of compounds and
  mixtures.
• Most elements are reactive and form compounds
  with other elements.
• Ex Na Cl ? NaCl
• Exceptions the noble gases (Group 8A) and the
  noble metals (gold, silver, platinum).
• Noble gases exist as single atoms.

11

• Some gases exist as diatomic molecules at normal
  temperatures
• (around 25o C)
• H2
• O2 and N2 are components of air
• The halogens -- F2, Cl2, Br2, I2
• However, hydrogen and the halogens are rarely
  present on earth in elemental form because they
  easily form compounds with other elements.
• Ex Na Cl ? NaCl
• Mg 2Br ? MgBr2
• 2H2 O2 ? 2H2O

12

• Only two elements are liquids at normal
  temperatures bromine (Br2) and mercury (Hg)
  metal.
• All other elements are solids at normal
  temperatures (around 25o C).
• (cesium and gallium melt at about 30o C)

13

• Allotropes
• Forms of a solid nonmetallic element with
  different physical properties.
• The different physical properties arise from the
  different arrangements of the atoms in the solid.
• Allotropes of carbon include
• diamond (hard)
• graphite (slippery)
• buckminsterfullerene
• large, soccer-ball-shaped molecules
• See fig 4.18

13
14
4.10 Ions

• A neutral atom has zero net charge because the
  number of its protons () equals the number of
  its electrons (-).
• Adding or removing electrons from an atom creates
  an ion an atom with a net positive or negative
  charge.
• When one or more electrons are lost by a neutral
  atom, an ion with a positive charge is formed,
  called an cation.
• Examples

15

• A cation is named using the parent name of the
  atom
• Na is the sodium ion (or sodium cation)
• Mg2 is the magnesium ion (or magnesium cation)
• When one or more electrons are gained by a
  neutral atom, an ion with a negative charge is
  formed, called an anion.
• Examples

16

• An anion is named by taking the root name of the
  atom and adding the suffix ide.
• Cl- is the chloride ion
• F- is the fluoride ion
• O2- is the oxide ion
• Ions are never formed by adding or removing
  protons to a nucleus.
• Isolated atoms do not form ions on their own.

17

• Ions form when metallic elements react with
  nonmetallic elements. The metal atoms lose one
  or more electrons, which are in turn gained by
  the atoms of the nonmetal.

18

• Ion Charges and the Periodic Table
• (See fig 4.19)
• Group 1A metals form 1 ions.
• Group 2A metals form 2 ions.
• Group 3A metals form 3 ions.
• Transition metals form cations with various
  charges. Examples
• Fe2 and Fe3
• Cu and Cu2
• Group 4A metals form cations with various
  charges
• Pb2 and Pb4
• Sn2 and Sn4
• Group 5A nonmetals form 3- ions.
• Group 6A nonmetals form 2- ions.
• Group 7A nonmetals form 1- ions