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Understanding Elemental Composition and Atomic Theory

Explore Dalton's symbols for elements, elemental composition of humans, metallic characters, and the building blocks of matter through the history of atomic theory. Learn about atomic structures, isotopes, and laws governing chemical composition.

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Understanding Elemental Composition and Atomic Theory

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  1. Atoms and Elements Chapter 4

  2. Dalton’s symbols for elements

  3. Element Names and Symbols • Element Ele • name symbol • 1 or 2 letters (occasionally 3) • 1st letter is capitalized, 2nd letter is lower case.

  4. Distribution of the common elements in nature. 3.2

  5. Elemental Composition of Humans (by mass)

  6. Metallic characters • Metal – shiny, high density, high melting point, great conductor of heat and electricity • Non-metal – dull, low density, low melting point, not good conductor of heat and electricity • Semi-metal – metal-like in appearance and has properties that are between that of a metal and a non-metal.

  7. What are the building blocks of matter? • Early Greeks • Air, Earth, Water, Fire • Democritus (470-370 BC) • Atoms • John Dalton (1766-1844) • Modern Atomic Theory

  8. Dalton’s Atomic Theory • Elements (matter) is composed of small, indivisible particles called atoms. • Atoms of a given element are identical in mass and behavior. • Atoms of different elements differ in mass and behavior. • Chemical combination of elements to make different substances occurs when atoms join together in small whole number ratios. • Chemical reactions only rearrange the way the atoms are combined; the atoms themselves are not changed.

  9. Law of Constant Composition • The law of constant composition states that the composition of a substance is always the same, regardless of how the substance was made or where the substance is found. • For example • All water is 11.3% H and 88.8% O

  10. Law of Multiple Proportions • If the same two elements(A and B) formed two different compounds, there is a whole number relationship between the masses of B in the two different compounds for each gram of A in the compound. • CO 12 g C 16 g O • CO2 12 g C 32 g O

  11. Sub Atomic Particles

  12. Atoms are composed of

  13. Isotopes • Atoms which differ only in the number of neutrons present in the nucleus. • Neutrons help keep the protons together by adding to the strong nuclear force without adding to the mutually repulsive electrical force of the protons. • Generally 1-1.5 neutrons per proton in an atom’s nucleus.

  14. Atomic Number = Z = number of protons in an atom. = number of electrons in a neutral atom. Mass Number = number protons + number neutrons in an atom

  15. Atomic Mass • The average relative mass of the isotopes of an element compared to the atomic mass of carbon-12 (exactly 12 amu) • Atomic mass unit (amu) • 1/12 the mass of a carbon-12 atom • 1.6606 x 10-24 g

  16. Isotopes of Neon

  17. Isotopes of Neon

  18. Chemical Formulas • AxByCz Elemental Symbol Number of atoms

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