The Structure of an Atom

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The Structure of the Atom

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Presentation transcript:

The Structure of an Atom Ch.4 Notes

Section 1: Early Theories of Matter Atom- the smallest particle of an element that retains the properties of the element. Size? The world’s population is 6,840,000,000 The number of atoms in a penny is 29,000,000,000,000,000,000,000

Early Theories of Matter Ancient Greek philosopher Democritus speculated matter was made up of atomos The theory was rejected for 2000 years due to being challenged by Aristotle

Discovery of the Electron John Dalton- proposed his atomic theory in 1803 based on his research that was not completely accurate Atoms can be subdivided Atoms of the same element can have slightly different masses

Discovering the Electron Sir William Crookes - used a cathode ray tube to do experiments on the atom based on the relationship between mass and charge. Electrons are negatively charged

Discovering the Atom JJ Thomson (1856-1940)- in the 1890’s found a cathode ray could be deflected by magnetic and electric fields. He concluded the ray was a stream of negatively charged particles dislodged from an atom with a mass much less than a hydrogen atom. http://www.youtube.com/watch?v=GzMh4q-2HjM

Discovering the Atom Robert Millikan (1868-1953) – in 1909 he accurately determined the mass of an electron through the Oil Drop Experiment, it had a charge of -1 The actual mass of an electron is 9.1 x 10-28 g

Nucleus Plum Pudding Theory-( aka the chocolate chip cookie model) Matter is neutral, so Thomson proposed: spherical atoms have uniform (+) charge with (-) electrons embedded throughout.

Nucleus Ernest Rutherford, in 1911 http://www.youtube.com/watch?v=wzALbzTdnc8 Ernest Rutherford, in 1911 To test the theory, he aimed a thin beam of (+) charged Alpha particles at a thin sheet of gold. He expected the alpha particles to pass through with little deflection Instead, most passed through, but few bounced back and deflected at big angles. He concluded atom is mostly empty space with large (+) charged nucleus in center

Atomic Summary *Nucleus -protons + neutrons -contains all the mass -positive charge *Electrons -located in the cloud -fast moving -very small

Properties of Subatomic Particles Relative Mass Actual Mass Particle Symbol Location Charge Electron Cloud e- 9.11 x 10-28 Electron -1 1/1840 p+ Nucleus +1 1 Proton 1.673 x 10-24 n0 Nucleus none 1 1.675 x 10-24 Neutron

How atoms differ: Atomic number is how an atom is identified, it is equal to the number of protons in an atom, & determines the location of the atom in the periodic table. The periodic table is arranged left to right & top to bottom by increasing atomic number.

atomic # 1 H Chemical Symbol 1.008 Average atomic mass

Atomic Number Number of protons in nucleus of an element This number identifies the element Periodic table is arranged in sequence of increasing atomic numbers Atoms are neutral: (+) charges must equal (-) charges

We know: atomic # = #protons = # electrons How many protons and electrons are there in: Be: p= 4 e= 4 F: p= 9 e= 9

Ions Be2+ has lost 2 electrons: F1- has gained one electron: p= 4 e= 2 Charged particles: Number of electrons has changed- proton # stays the same Be2+ has lost 2 electrons: F1- has gained one electron: p= 4 e= 2 p=9 e=10

Isotopes To identify an isotope a number is added to the end of the name, it is called a mass number. Mass Number = # of protons + # of neutrons Ex: Carbon-14, Neon-22, Potassium-41

Isotopes All atoms of same element have some number of protons Most have different numbers of neutrons

Mass Number An isotope is identified by its mass number Mass number= number of protons + number of neutrons Number of neutrons = mass number – atomic number

Atomic Mass Atomic mass units (amu) = ½ the mass of a Carbon-12 atom Atomic mass given in Periodic Table is not given in whole numbers Atomic mass is the weighted average of the atomic masses of all naturally occurring isotopes. This weighted average takes into account the mass and abundance of each isotope

Atomic Mass Average atomic mass= mass * abundance for each isotope: then add Copper-63 Copper-65 Number of protons 29 Number of neutrons 34 36 Atomic mass 62.930 amu 64.928 amu Abundance 69.17% 30.83%

Mass Contribution = mass x abundance Cu-63= (62.930)(.6917)= 43.53 Cu-65= ( 64.928)(.3083) =20.02 43.53+20.02= 63.55