Presentation on theme: "Definition of Atoms Atoms are the fundamental building blocks of all matter, not able to be split by ordinary chemical reactions greek word atomos which."— Presentation transcript:
Definition of Atoms Atoms are the fundamental building blocks of all matter, not able to be split by ordinary chemical reactions greek word atomos which means “indivisible”. This is based upon the discontinuous theory of matter. (meaning matter can not continually be split and still remain the same)
HISTORY OF THE ATOM 460 BC Democritus develops the idea of atoms he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called ATOMA (greek for indivisible)
HISTORY OF THE ATOM Aristotle modified an earlier theory that matter was made of four “elements”: earth, fire, water, air. Aristotle was wrong. However, his theory persisted for 2000 years. Aristotle fire air water earth 350 BC
HISTORY OF THE ATOM 1808 John Dalton suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMIC THEORY All matter is made of atoms. Atoms of an element are identical. Each element has different atoms. Atoms of different elements combine in constant ratios to form compounds. Atoms are rearranged in reactions
HISTORY OF THE ATOM 1898 Joseph John Thompson found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON
HISTORY OF THE ATOM Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge 1904 like plums surrounded by pudding. PLUM PUDDING MODEL
HISTORY OF THE ATOM 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
HISTORY OF THE ATOM 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
HISTORY OF THE ATOM 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.
HISTORY OF THE ATOM 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.
HELIUM ATOM + N N + - - proton electron neutron Shell What do these particles consist of?
ATOMIC STRUCTURE Particle proton neutron electron Charge + 1 charge -1 charge 0 1amu 1/1836 Mass Amu = atomic mass unit 1 amu = 1.66 x 10 -24 g
Relative Sizes Thus 99.99% of the mass of an atom comes from the nucleus (protons and neutrons) and essentially nothing from e- the major volume of atoms coming from the electron cloud Remember that most of the atom is empty space like spinning blades of a fan take up more space than any blade would if not moving
ATOMIC STRUCTURE the number of protons and neutrons in an atom the number of protons in an atom He 4 2 Atomic number Atomic mass number of electrons = number of protons
Calculating subatomic particles p+ = atomic number n 0 = mass # - p+ because mass of atom is p+ + n 0 get the mass # by rounding average atomic mass on periodic table to nearest whole number if needed e- = p+ - charge because charge of atom/ion is p+ - e-
Protons, Electrons, Neutrons Determine the number of protons, electrons and neutrons for each of the following elements; Ca O ClSi Na 40 20 23 11 16 35 8 17 28 14 B 5 11 a)b)c) d)e)f) P=20 e=20 n=20 p=11 e=11 n=12 p=17 e=17 n=18 p=14 e=14 n=14 p=5 e=5 n=6 p=8 e=8 n=8
Equations: Protons = atomic #, neutrons = mass # - protons, electrons = protons with a neutral atom (charge = 0) electrons = protons – charge with a ion (charged atom) SymbolprotonsMass #neutronselectrons 7 Li atom 3 p + the atomic # 7 amu7-3 = 4 n 0 3 e - (same as p + ) Cs atom Rb atom 32 Cl -1 ion Al -3 ion 42 Ca +2 ion
Equations: mass # = atomic mass rounded to nearest whole Protons = atomic # Neutrons = mass # - protons with a neutral atom (charge = 0) the electrons = protons, with a ion (charged atom) the electrons = protons – net charge SymbolprotonsMass #neutronselectrons 7 Li atom3 p + the atomic # 7 amu7-3 = 4 n 0 3 e - (same as p + ) Cs atom551337855 Rb atom37854837 32 Cl -1 ion17321518 Al -3 ion13271416 42 Ca +2 ion 20422218
Isotopes Carbon-12 Carbon-13 Carbon-14 Protons 6 6 6 6 7 8 Neutrons Mass # 12 13 14 Atoms with same atomic number (number of protons), but with different masses (due to different number of neutrons) 12-6 = 6 13-6 = 714-6 = 8
Lithium Isotopes Li-6 is the chemical symbol for Lithium with a mass number of 6 amu. (this is 3 protons plus 3 neutrons in nucleus. Li-7 has 3 protons and 4 neutrons in nucleus and a mass of 7 amu. The atomic mass (or average weight) of Lithium is 6.941. Therefore which isotope is most abundant in nature?
IONS IONS are atoms or groups of atoms with a positive or negative charge.IONS are atoms or groups of atoms with a positive or negative charge. Taking away an electron from an atom gives a CATION with a positive chargeTaking away an electron from an atom gives a CATION with a positive charge Adding an electron to an atom gives an ANION with a negative charge.Adding an electron to an atom gives an ANION with a negative charge. To tell the difference between an atom and an ion, look to see if there is a charge in the superscript! Examples: Na + Ca +2 I - O -2To tell the difference between an atom and an ion, look to see if there is a charge in the superscript! Examples: Na + Ca +2 I - O -2 Na Ca I O Na Ca I O
Forming Cations & Anions A CATION forms when an atom loses one or more electrons.A CATION forms when an atom loses one or more electrons. Mg --> Mg2+ + 2 e- An ANION forms when an atom gains one or more electrons F + e- --> F-
PREDICTING ION CHARGES In general metals (Mg) lose electrons ---> cationsmetals (Mg) lose electrons ---> cations Nonmetals (F) gain electrons anionsNonmetals (F) gain electrons anions
Ion Practice State the number of protons, neutrons, and electrons in each of these ions. 39 K + 16 O -241 Ca +2 198 20 #p + 19 8 20 #n o 20 8 21 #e - 18 10 18
Charges on Common Ions -2-3 +1 +2 By losing or gaining e-, atom has same number of e-’s as nearest Group 8A atom.
Special Family Names on the Periodic Table Alkali Metals = hot orangeSemimetals/Metalloids = pink Alkaline Earth Metals = Faded BlueHalogens = Yellow Transition Metals = IndigoNoble Gases = Pumpkin Orange Other Metals = Baby BlueOther Nonmetals = Green
3 p + 4 n 0 2e – 1e – Li shorthand Bohr - Rutherford diagrams Putting all this together, we get B-R diagrams To draw them you must know the # of protons, neutrons, and electrons (2,8,8,2 filling order) Draw protons (p + ), (n 0 ) in circle (i.e. “nucleus”) Draw electrons around in shells 2 p + 2 n 0 He 3 p + 4 n 0 Li Draw Be, B, Al and shorthand diagrams for O, Na
11 p+ 12 n° 2e – 8e – 1e – Na 8 p+ 8 n° 2e – 6e – O 4 p+ 5 n° Be 5 p+ 6 n° B 13 p+ 14 n° Al
ATOMIC STRUCTURE Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. first shella maximum of 2 electrons second shella maximum of 8 electrons third shella maximum of 8 electrons
ATOMIC STRUCTURE There are two ways to represent the atomic structure of an element or compound; 1.Electronic Configuration 2.Dot & Cross Diagrams
ELECTRONIC 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 7 2 in 1 st shell 5 in 2 nd shell configuration = 2, 5 2 + 5 = 7
ELECTRONIC CONFIGURATION Write the electronic configuration for the following elements; Ca O ClSi Na 40 20 23 11 16 35 8 17 28 14 B 5 11 a)b)c) d)e)f) 2,8,8,22,8,1 2,8,72,8,42,3 2,6
DOT & 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 14 7
DOT & CROSS DIAGRAMS Draw the Dot & Cross diagrams for the following elements; OCl 1635 8 17 a)b) O X X X X X X X X Cl X X X XX X X X X X X X X X X X X X
SUMMARY 1. The Atomic Number of an atom = number of protons in the nucleus. 2. The Atomic Mass of an atom = number of Protons + Neutrons in the nucleus. 3. The number of Protons = Number of Electrons. 4. Electrons orbit the nucleus in shells. 5. Each shell can only carry a set number of electrons.