Ch 5 Atoms Molecule Formulas Subatomic Particles Atoms

Ch # 5 Atoms, Molecule, Formulas, Subatomic Particles.

Atoms § An atom is the smallest particle of an element that can exist and still have properties of the element.

Atomic Theory of Matter § All matter is made up of small particles called atoms. 113 types. § Atoms of same element are similar to one another. § The relative number and arrangement of different types of atoms contained in a pure substance determined its identity.

Atomic Theory of Atoms. § These atoms rearrange, separate or unite to form a new substance. § Atoms can participate in or result from any chemical change, atoms cannot be destructed.

An atom is very Small

The diameter of an atom is 0. 1 to 0. 5 nm. This is 1 to 5 ten billionths of a meter. If the diameter of this dot is 1 mm, then 10 million hydrogen atoms would form a line across the dot.

The Molecule § A group of two or more atoms that is strongly bound to each other.

The Molecule § Diatomic molecule: contains 2 atoms. H, N, O, F, Cl, Br, I, § Triatomic molecule: Contains 3 atoms. § P-4 atoms, S-8 atoms. § Homoatomic molecule: All atoms are of same kind. § Heteroatomic molecule: Two or more different kinds of atoms are present.

Molecular compounds § Compounds that have heteroatomic molecule as basic structural unit. § Ex: table sugar-sucrose. § Molecule is a limit of physical subdivision. Atom is a limit of chemical sub-division.

Molecular Compounds § Two kinds of atoms present, but, one kind of molecule. § Molecules have different properties than that of the atom.

Ionic compounds § Compounds that contain ions. Ex: Na. Cl

Natural and Synthetic compounds § The compounds could be naturally or artificially made.

Chemical Formulas § Made up of symbols. § The subscripts indicate the number of atoms. § Read the formula C 6 H 12 O 6

Protons

• Eugen Goldstein, a German physicist, first observed protons in 1886: § Thompson determined the proton’s characteristics. § Thompson showed that atoms contained both positive and negative charges. § This disproved the Dalton model of the atom which held that atoms were indivisible.

Subatomic Particles. § Protons: +ve charge. -Goldstein. Charge: +1 § Electron: -ve charge. - Thomson. Smallest mass. Charge: -1 § Neutron: No charge. -Chadwick. § Opposite charges attract, like charges repel.

Nucleus: § Small, dense, positively charged center of an atom. It contains protons and neutrons. An atoms entire mass is concentrated to the center.

Nucleon § Any subatomic particle found in the nucleus of an atom. Ex; protons and neutrons. § Electrons revolve around the nucleus in a very large region. It is mostly empty space. § Volume occupied by electrons is called electron cloud. It is negatively charged.

An atom as a whole is neutral. Number of protons=Number of electrons in any atom. The +ve and-ve charges cancel each other out.

Diameter of nucleus= 10 -15 m. Entire mass is concentrated in the center of the atom.

Protons and neutrons are made of Leptons, Mesons, Baryons.

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Atomic Numbers of the Elements

• The atomic number of an element is equal to the number of protons in the nucleus of that element. § The atomic number of an atom determines which element the atom is.

atomic number of 1 is a hydrogen atom. Every hydrogen atom contains 1 proton in its nucleus.

atomic number Every atom with an atomic number of 6 is a carbon atom. 6 protons in the nucleus C 6

atomic number Every atom with an atomic number of 1 is a hydrogen atom. 1 proton in the nucleus H 1

Isotopic Notation

Isotopes of the Elements

• Atoms of the same element can have different masses. § They always have the same number of protons, but they can have different numbers of neutrons in their nuclei. § The difference in the number of neutrons accounts for the difference in mass. § These are isotopes of the same

Isotopes of the Same Element Have Equal numbers of protons Different numbers of neutrons

Hydrogen has three isotopes 1 proton 0 neutrons 1 neutron 2 neutrons

Examples of Isotopes Element Protons Electrons Neutrons Symbol Hydrogen 1 1 1 0 1 2 1 1 H 2 H 1 3 H 1 Uranium 235 U 92 Uranium 238 U 92 92 92 143 92 92 146 Chlorine 35 Cl 17 17 17 18

Atomic Mass

• The mass of a single atom is too small to measure on a balance. § Using a mass spectrometer, the mass of the hydrogen atom was determined.

Using a mass spectrometer, the mass of one hydrogen atom was determined to be 1. 673 x 10 -24 g.

This number is very small small small small small small

A Modern Mass Spectrometer Positive ions formed from sample. Electrical field From the intensity and positions at slits A mass of the lines on the Deflection of mass accelerates spectrogram, theionsdifferent positive ions. positive is recorded. isotopes and relative occurstheir at amounts can be determined. magnetic field. 5. 8

The standard to which the masses of all other atoms are compared to was chosen to be the most abundant isotope of carbon.

1 amu is defined as exactly equal to the mass of a carbon-12 atom 1 amu = 1. 6606 x 10 -24 g

Average atomic mass 1. 00797 amu.

Average atomic mass 248. 029 amu.

Average Relative Atomic Mass

• Most elements occur as mixtures of isotopes. § Isotopes of the same element have different masses. § The listed atomic mass of an element is the average relative mass of the isotopes of that element compared to the mass of carbon-12 (exactly 12. 0000…amu).