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CHEMISTRY

CHEMISTRY. Elements are made of ATOMS The Atom. The Atom. H istory. 450 BC – Greeks describe matter as being made of small, indestructible atoms 1704 – Newton described matter as being made of indivisible particles

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CHEMISTRY

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  1. CHEMISTRY Elements are made of ATOMS The Atom

  2. The Atom • History • 450 BC – Greeks describe matter as being made of small, indestructible atoms • 1704 – Newton described matter as being made of indivisible particles • 1803 – John Dalton describe each element being unique because each is made of its own atom • Modern Atomic Theory – • Each element has its own atom

  3. The Atom • Structure • The Atom contains charged particles • Particles with different charges attract each other • Particles with same charges repel each other • Atom consists of: • Protons positive charge • Electrons negative charge • Neutrons NO charge

  4. The Atom • Structure • The Atomic Model • Nucleus – center of the atom- contains protons and neutrons • Electron Cloud – surrounds the nucleus – contains the electrons • Atoms are extremely small, millions can fit on this .

  5. The Atom • The Nucleus ~ • Protons • Positively charged • Unique to each element • The identity of an element is determined by the number of protons ~ Atomic Number • Every atom of each element will have the same number

  6. The Atom • The Nucleus ~ • Neutrons • NO charge • Number of neutrons can change • Elements that have different number of neutrons are called Isotopes • Isotopes are identified by their Atomic Mass*

  7. The Atom • The Electron Cloud ~ • Electrons • Negative charge • Number of electrons can change • When an atom loses or gains an electron an ion* is formed, this will change the charge of the atom • Electrons move extremely fast • Mass of electrons is very small

  8. The Atom • Atomic Mass and Isotopes • Total number of protons and neutrons • When the number of neutrons change so will the atomic mass, the element will be named by its atomic mass – an isotope is formed • Example Chlorine has 17 protons, but the number of neutrons can change Clorine-35 (18 neutrons) and Clorine-37(20 neutrons)

  9. The Atom • Ions • Electrons fill up around the nucleus in a configuration called the electron shell (each shell holds a given amount of electrons)

  10. The Atom • Ions • Groups 1 and 2 will lose electrons so their outer shell is full • Groups 16 and 17 will gain electrons to fill up their outer shell

  11. The Atom • Ions • Lost electrons • Form a POSITIVE ION – • The atom now has more protons than electrons • Size of the atom becomes smaller • Represented by a raised plus sign next to the symbol • Na+ • Ca2+

  12. The Atom • Ions • Gained electrons • Form a NEGATIVE ION – • The atom now has more electrons than protons • Size of the atom becomes larger • Represented by a raised negative sign next to the symbol • Cl- • O2-

  13. Atom • Change in protons • Radioactive elements – • When an element has too many or too few neutrons the nucleus becomes unstable • To become stable energy is released in the form of protons • When protons are lost it becomes a new element – radioactive decay (half-life) • Each element has its own unique half life – how long it takes to change from one element to another

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