Back to the macroscopic world

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Nuclear fusion within the Sun:

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• Proton: positively charged, found in nucleus of the atom • Neutron: neutral, found in nucleus of atom • Positron: positive charge, antiparticle of electron • Neutrino: neutral, interacts only weakly, small mass • Gamma ray: highly-energetic photon

Week 3a

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Hydrogen Helium

Proton

Carbon

Produced in supernovae

Nuclear fusion in the sun and early big bang nucleosynthesis 3 minutes H+H He

Beta decay Alpha particle

Alpha decay

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99 % consists of:

Oxygen

Carbon

Hydrogen

Nitrogen

Calcium

Phosphorus

98 % of matter in the universe is hydrogen and helium

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Atoms are neutral

Number of electrons equals number of protons

Nucleus consists of protons and neutrons in (approximately) equal numbers

Atomic number (Z): number of protons

Mass number (A): number of p+n

Number of neutrons (N=A-Z) may vary: isotope

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6p+6n 6p+7n 6p+8n

Isotopes have similar chemical properties.

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(0.7 %)

(99,3 %)

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Atomic number, Z

Atomic weight (close to A)

Russian chemist Dmitri Mendeleev in 1869

Illustrates recurring ("periodic") trends in the properties of the elements

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Bohr’s model: Nucleus has internal structure:

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Build up of the periodic table based on few simple physical principles:

Total number of electrons such that atom is neutral.

Electrons in discrete orbits, as in Bohr’s model.

Orbit has “quantum number”. Determines:

Energy

Size of the orbital

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Each orbital specific number of electrons:

Pauli exclusion principle: no two electrons in the same state. At most two electrons in each orbital.

There are suborbitals, wich give two extra quantum numbers

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: s-orbital. Max: 2 electrons : p-orbital. Max: 6=2x3 electrons : d-orbital. Max: 10=2x5 electrons : f-orbital. Max: 14=2x7 electrons

Total:

• The quantum states

are called orbitals. • States with the same

are called shells (have the same energy). • Each orbital has

electrons, hence:

shell can host

electrons

shell can host

electrons

shell can host

electrons, etc.

• This should give the length of each row of the periodic table (2,8,18, etc.). • There are exceptions due to screening of electrons. The actual lengths are

(2,8,8,18, etc.)

The Periodic Table is based on the observation that an element's chemical properties depend on the number of electrons in its outer shell.

You can count to see how many electrons are in the outer unfilled shell. Elements with the same number of electrons in their outer shell are grouped together.

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Halogens: • Highly reactive, harmful or lethal to biological organisms. • Reactivity due to the atoms being highly electronegative. They can gain an

electron by reacting with atoms of other elements. • Fluorine one of the most reactive elements, attacking otherwise inert

materials such as glass. Corrosive, highly toxic gas. • Once it does react with something, it bonds so strongly that resulting

molecule is very inert and non-reactive. For example, Teflon is fluorine bonded with carbon.

• Chlorine and bromine used as disinfectants for drinking water, swimming pools, fresh wounds, dishes, and surfaces. They kill bacteria and microorganisms.

Atoms (or molecules) in which number of electrons does not equal number of protons.

Electrically charged.

: has lost one electron.

: has gained one electron.

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The periodic table is the alphabet or genetic code in which we can write “words”.

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Atoms Periodic table Molecules

Letters Alphabet Words

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Next level of complexity: the words of chemistry (molecules) become the letters of biology.\ Big Questions in Science, fall 2012. SdH, AUC 24

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Subatomic particles Atom: nucleus and electrons. Strong and

electrical force. Molecules. Periodic table. Electrical force.

Emerging: van der Waals forces between molecules.

Substances, tissues. Electrical force.

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