, who was from was the first person to use the term atom during B.C.  Democritus defined the atom as being.  opposed Democritus because believed that.

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Presentation transcript:

, who was from was the first person to use the term atom during B.C.  Democritus defined the atom as being.  opposed Democritus because believed that atoms and that matter was. Democritus Greece 400 indivisible Aristotle did not exist continuous

 Chemists accepted the modern definition of an element during the late.  An is a substance that cannot be broken down by ordinary chemical means.  Chemists could not agree whether elements always combine in the when forming a compound. 1700s element same ratio

 Chemists studied during the 1790s in order to find out whether elements always combine in the same ratio.  They discovered the law of, which states that chemical reactions conservation of mass

 Chemists studied during the 1790s in order to find out whether elements always combine in the same ratio.  They discovered the law of, which states that cannot be or during chemical and physical changes. chemical reactions conservation of massmass createddestroyed

45 g H 2 O Dorin, Demmin, Gabel, Chemistry The Study of Matter, 3 rd Edition, 1990, page 204 High voltage Before reaction electrodes glass chamber 5.0 g H 2 80 g O g total H2H2 O2O2 High voltage After reaction 0 g H 2 40 g O g total O2O2 H2OH2O

 The law of definite proportions deals with the compound.  The fact that a compound consists of the percentages by regardless of of each element you start with, the compound is formed, or the compound is formed. same always same mass how much where how

 In the laboratory…  In nature… (copper ore in Nevada) % copper 38.85% oxygen copper carbonate 9.72% carbon 51.44% Cu 38.85% O 9.72% C

 The law of multiple proportions states: when two of the elements combine to form compounds and the first element has a mass, the of masses between the element will be a number. same different fixed ratio second element whole

 Two compounds containing carbon and oxygen Carbon monoxide (CO) Carbon dioxide (CO 2 ) 1.0g C 1.33g O 1.0g C 2.66g O

1. All matter is made up of. 2. Atoms of the element are and atoms of elements are. 3. Atoms cannot be,, or. 4. Atoms of different elements combine in to form compounds. 5. In chemical reactions, atoms are, or. atoms same identicaldifferent subdivided different createddestroyed whole-number ratios combined separatedrearranged

1. All matter is made up of. 2. Atoms of the element are and atoms of elements are. 3. Atoms cannot be,, or. 4. Atoms of different elements combine in to form compounds. 5. In chemical reactions, atoms are, or. atoms same identicaldifferent subdivided different createddestroyed whole-number ratios combined separatedrearranged 2. Atoms of different elements are different

 conducted the cathode ray experiment in. Joseph John (J.J.) Thomson 1897

Cathode Ray Experiment + - Cathode ray tube metal disks are tubes that are filled with low pressure gas and contain two metal disks. Cathode ray tubes

Cathode Ray Experiment + - vacuum tube metal disks voltage source

Cathode Ray Experiment + - voltage source OFF ON Passing an electric current through a cathode ray tube causes the tube to. glow

The glow was caused by a of called a cathode ray. A cathode ray is by a magnetic field. stream particles deflected

 Thomson measured the ratio of the cathode ray particles and found that this ratio was ALWAYS the for every element.  Thomson concluded that cathode rays are composed of identical. charged. charge:mass same negatively particles

 studied electrons in.  Millikan found that the of an electron is of the mass of a atom.  He confirmed that an electron carries a charge.  Millikan concluded that are present in atoms of elements. Robert A. Millikan 1909 mass 1/2000 hydrogen negative electrons all

 The discovery of the electron led chemists to infer the following during the early 1900s: ◦ Atoms must contain a charge in order to the because atoms are electrically. ◦ Atoms must contain other that account for most of their because of the tiny mass of the electron positive balance electrons neutral particles mass

 conducted the gold foil experiment in.  are positively charged particles.  Rutherford and associates shot a thin piece of with fast-moving.  They assumed that and were distributed throughout the gold foil. Rutherford and associates 1911 Alpha particles gold foil alpha particles mass charge uniformly

What he expected… He expected that the alpha particles would the gold foil pass through

What he got… He found that the of the alpha particles passed through while other alpha particles were majority redirected

 Rutherford explained that the alpha particles were redirected because they experienced a, which occupies a very of space.  He concluded that the force was due to a bundle of matter with a charge, which he called the. powerful force small amount dense positive nucleus

 observed cathode ray tubes in and found rays that traveled in the direction of cathode rays  He concluded that these oppositely traveling rays contained charged particles.  discovered the existence of the in. Goldstein 1886 opposite positively Chadwick neutron 1932

Subatomic Particle Charge Mass number Proton Neutron Electron

Subatomic Particle Charge Mass number Proton +1 Neutron Electron

Subatomic Particle Charge Mass number Proton +1 Neutron 0 Electron

Subatomic Particle Charge Mass number Proton +1 Neutron 0 Electron

Subatomic Particle Charge Mass number Proton +1 1 Neutron 0 Electron

Subatomic Particle Charge Mass number Proton +1 1 Neutron 0 1 Electron

Subatomic Particle Charge Mass number Proton +1 1 Neutron 0 1 Electron 0

 Atoms are electrically neutral because they contain the number of and.  The nuclei of atoms of different elements differ in the. same protons electrons number of protons

 Atoms with two or more protons do not fall apart because there is a strong between them.  The are the short- range forces between protons and protons, neutrons and neutrons, and protons and neutrons that hold the nucleus together. attraction nuclear forces

 The is a region occupied the electrons.  Atomic radii are expressed in and they range from to in length. electron cloud picometers (pm) 40pm270pm

 What are the two most important ideas of Dalton’s atomic theory?  Which of the following did Thomson NOT discover about the cathode ray? a)The charge to mass ratio of a cathode ray is large b)The mass of a cathode ray is 1/2000 the mass of a hydrogen atom c)Cathode rays are made up of negatively charged particles  What did Rutherford NOT discover about an atom? a)The nucleus contains neutrons b)The nucleus contains positively charged particles c)The volume of a nucleus is very tiny