Download Atomic Structure - MsReenChemistry

ATOMIC STRUCTURE
Bhavya, Seoyeong, Eric
THE NUCLEAR ATOM
• All matter is composed of tiny indivisible particles called atoms
• Atoms cannot be created or destroyed
• Atoms of the same element are alike in every way
• Atoms can combine together in small numbers to form molecules
• They contain a positively charged dense nucleus consisting of protons and neutrons
(nucleons)
• Negatively charged electrons occupy the space outside the nucleus
• Atoms have large amounts of empty space
THE NUCLEAR ATOM
• The electrostatic force of attraction between the oppositely charged subatomic particles prevents the electron from leaving the atom.
• The existence of neutrally charged neutrons is crucial for the stability of
nuclei
Sub atomic particles
Relative Mass
Relative
Charge
1
+1
Neutrons
0.0005
-1
Electrons
1
0
Protons
THE NUCLEAR ATOM
• Atomic number – Number of protons in the nucleus (Ar)
• Mass number – Number or protons + neutrons in an atom (Mr)
• Isotopes – Atoms of the same element with same number of protons but different
number of
• neutrons
• Ions – When an atom loses electrons it becomes a positive ion (Cation), when it
gains electrons negative ions (Anions) are formed.
ISOTOPES AND IONS
Examples:
• Two isotopes of chlorine – Cl-35 and Cl-37. In a sample of a 100 Cl atoms 77.5 are
atoms Cl-35 and 22.5 are Cl-37. Find the RAM.
0.775*35 + 0.225*37 = 35.45
•
MASS
SPECTRA
• An instrument known as a mass spectrometer can be used to measure the mass of
individual atoms, e.g. mass of a hydrogen atom is 1.67*10^-24g. Because all the
masses are so small (in the range 10^-24 to 10^-22) it makes more sense to use
relative values, so C-12 is the chosen standard.
• The results of the analysis by the mass spectrometer are presented in the form of a
mass spectrum.
• Horizontal axis – shows mass/charge ratio of the different ions on the C-12 scale,
which in most cases can be considered to be equivalent to their mass.
• Vertical axis – percentage abundance of ions
• Relative average mass = total mass/no. of atoms
Mass spectrum of gallium. The no. of lines indicate the no. of isotopes.
We can use this info. to calculate the RAM of an element.