Published on March 15, 2014
CHEMISTRY PROJECT BY COMPUTERCAREERS
What is an Atom? • Matter is anything that takes up space and has mass. • All matter is made of atoms • Atoms are the building blocks of matter, sort of how bricks are the building blocks of houses.
Parts of Atom • An atom has three parts: • Proton = positive • Neutron = no charge • Electron = negative • The proton & neutron are found in the center of the atom, a place called the nucleus. • The electrons orbit the nucleus.
ATOMIC STRUCTUREATOMIC STRUCTURE Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. • first shell a maximum of 2 electrons • second shell a maximum of 8 electrons • third shell a maximum of 8 electrons
ATOMIC STRUCTUREATOMIC STRUCTURE There are two ways to represent the atomic structure of n element or compound; 1. Electronic Configuration 2. Dot & Cross Diagrams
ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION With electronic configuration elements are represented numerically by the number of electrons in their shells and number of shells. For example; N Nitrogen 14 2 in 1st shell 5 in 2nd shell configuration = 2 , 5 2 + 5 = 7 7
DOT & CROSS DIAGRAMSDOT & CROSS DIAGRAMS With Dot & Cross diagrams elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example; Nitrogen N XX X X XX X N 7 14
1910 Ernest Rutherford oversaw Geiger and Marsden carrying out his famous experiment. they fired Helium nuclei at a piece of gold foil which was only a few atoms thick. they found that although most of them passed through. About 1 in 10,000 hit
Rutherford’s InventionRutherford’s Invention gold foil helium nuclei They found that while most of the helium nuclei passed through the foil, a small number were deflected and, to their surprise, some helium nuclei bounced straight back. helium nuclei
Rutherford’s new evidence allowed him to propose a more detailed model with a central nucleus. He suggested that the positive charge was all in a central nucleus. With this holding the electrons in place by electrical attraction However, this was not the end of the story.
ARISEN OF NEILS BOHRARISEN OF NEILS BOHR 1913 Niels Bohr studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons.
Rutherford’s alpha scattering experiment source of alpha particles Thin gold foil Photographic film Beam of α particles most pass straight through 1 in 20 000 deflected
Rutherford’s explanation atoms of gold in gold foil Path of an α particle nucleus of gold atom All these α particles pass straight through the empty space that makes up most of the atom. This α particle passes close enough to nucleus to be repelled As α particles are positively charged, the nucleus must contain positively charged protons.
atoms of gold in gold foil nucleus of gold atom As only 1 in every 20 000 α particles are repelled the nucleus must be very small. Size of the nucleus
Rutherford’s model of the atom Tiny nucleus containing the positively charged protons. Rest of atom is mostly empty space. The negatively charged electrons are spinning round the nucleus.
Section 3.1 The Limitations of Rutherford’s Atomic Model Chapter 3: Atomic Models and Properties of Atoms • radiation must be emitted, so it was expected that a continuous spectrum of light energy was being given off • because of radiation, the electron would lose energy and its orbit would decrease until it spiraled into the nucleus, destroying the atom
Bohr Model of Atom • The Bohr Model shows all of the particles in the atom. • In the center is circles. Each circle represents a single neutron or proton. Protons should have a plus or P written on them. Neutrons should be blank or have an N. • In a circle around the nucleus are the electrons. Electrons should have a minus sign or an e. ++ ++ -- --
Bohr’s Atom electrons in orbits nucleus
Bohr's Model of the Atom Bohr's model: -electrons orbit the nucleus like planets orbit the sun -each orbit can hold a specific maximum number of electrons -electrons fill orbits closest to the nucleus first.
Bohr's Model of the Atom Niels Bohr (1913): -studied the light produced when atoms were excited by heat or electricity Rutherford's model couldn't explain why unique colours were obtained by atoms of different elements Bohr proposed that electrons are in orbits & when excited jump to a higher orbit. When they fall back to the original they give off light
Bohr's Model of the Atom e.g. fluorine: #P = #e- = #N = 9 9 10 9P 10N
Today’s quantum mechanical model of the atom incorporates the wave properties of electrons. Section 3.2 The Quantum Mechanical Model of the Atom An electron density diagram represents an atomic orbital. Chapter 3: Atomic Models and Properties of Atoms Wave functions, initially described by Erwin Schrodinger, represent a region in space around a nucleus where an electron will be found. This region of space is called an atomic orbital
Section 3.2 The Quantum Mechanical Model of the Atom The circle does not represent a real boundary. Chapter 3: Atomic Models and Properties of Atoms Atomic orbitals can be visualized as “fuzzy clouds” • The higher the density of the “cloud,” the higher the probability of finding an electron at that point. • The cloud has no definite boundary. • The region where an electron will spend 90 percent of its time is depicted by drawing a circle.
Section 3.1 Quantum Numbers Describe Orbitals Chapter 3: Atomic Models and Properties of Atoms Electrons in the quantum mechanical model of the atom are described using quantum numbers. Three quantum numbers describe the distribution of electrons in the atom and a fourth describes the behaviour of each electron. Symbols for the four quantum numbers: n l ml ms
Section 3.2 The Principle Quantum Number, n Chapter 3: Atomic Models and Properties of Atoms • Is the first quantum number • Describes the energy level, or shell, of an orbital • All orbitals with the same n value are in the same shell • The larger the n value, the larger the size of the shell • Values can range from n = 1 to n = ∞ n = 1 first shell n = 2 second shell n = 3 third shell n = 4 fourth shell
Section 3.2 The Orbital-Shape Quantum Number, l Chapter 3: Atomic Models and Properties of Atoms • Is the second quantum number • Describes the shape of an orbital • Refers to energy sublevels, or subshells • Values depend on the value of n. They are positive integers from 0 to (n – 1) • Each value is identified by a letter l = 0 orbital s l = 1 orbital p l = 2 orbital d l = 3 orbital f An energy sublevel is identified by combining n with the orbital letter. For example, n = 2, l = 1: 2p sublevel
Section 3.2 The Magnetic Quantum Number, ml s, p, and d orbitals have characteristic shapes. Chapter 3: Atomic Models and Properties of Atoms • Is the third quantum number • Indicates the orientation of the orbital in space • For a given l there are (2l +1) values for ml • The total number of orbitals for an energy level is n2
NucleusNucleus 11stst shellshell 22ndnd shellshell 33rdrd shellshell
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