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Chemistry unit 1

1. Atomic structure

QuestionAnswer
Element a substance whose atoms all have the same number of protons made of only one kind of atom and cannot be broken down into simpler substances
Theory substituted for those parts of reality that are not yet discovered or understood and proposes an explanation for the phenomenon
acceptable theories should be logical and show congruence between the present body of knowledge and theoretical constructs
data collected must be accurate, reliable and replicable
as the body of knowledge increases theoretical adjustments must be made to overcome contradictions within the scientific society
1808 John Dalton developed the first useful atomic theory of matter. Some of Dalton's theories are now known to be incorrect but the basic concepts are the foundations of modern science
With the discovery of subatomic particles it was possible to show that the atom could be divided into smaller parts
indivisible unable to be divided or separated
atom Smallest particle of an element
molecule a particle that contains 2 or more atoms chemically joined together
Cathode rays consist of electrons
Electrons negatively charged particles about 1840 times lighter than hydrogen atoms
1897 JJ Thomson discovered electrons
Thomson work made it apparent that atoms were not indivisible and gave evidence for the existence of subatomic particles
the model that JJ Thomson propose Plum pudding model which described atoms as negative charged electrons embedded in a sphere of positive charge
Rutherford proposed that most of the atom must be mainly empty space with the mass and positive charge being concentrated in a tiny nucleus while the electrons orbit the nucleus like planets orbit the sun.
Rutherford planetary model of the atom did not explain why the negative electron revolving a positive nucleus did not lose energy and spiral into the nucleus or what prevented the electrons from being pulled into the nucleus by electrostatic attraction
the word atom comes from the greek "atomos" which means something that cannot be split into smaller pieces
atoms are considered ____ and consist of_______ the building blocks of chemistry______ protons, neutrons and electrons
where protons, electrons and neutrons are found held in a tiny nucleus by powerful nuclear forces while the electrons are found orbiting the nucleus
The mass of the subatomic particles is measured relative to one twelfth the mass of a carbon-12 isotope
the charge of the particles is compared to the charge of a proton and an electron
mass of proton 1 amu
mass of neutron 1 amu
Mass of an electron 1/1837
Charge of a proton +1
charge of a neutron 0
charge of a electron -1
the structure of the atom is held together by the electrostatic force of attraction between the + charged nucleus and the - charged electrons surrounding it
Atoms are electrically neutral species so the number of protons must be equal to the number of electrons
Atomic (proton) number the number of protons in the nucleus of an atom
the atomic number is used to define the atom because Atoms of the same element have the same number of protons
atomic mass/mass number the sum of protons and neutrons in the nucleus of the atom
the atomic mass is also referred to as the nucleon number since the protons and neutrons are found in the nucleus of the atom
who discovered isotopes Thomson found isotopes in 1913 when he saw that some atoms of the same elements had different masses
Isotopes atoms with the same atomic number but different mass numbers
Isotopes of an element have the same atomic number because they have the same number of protons but the difference in mass numbers is due to the different numbers of neutrons present
Why isotopes have the same chemical properties but different physical properties Since the number of protons is equal to the number of electrons, isotopes have identical chemical properties, however, their physical properties are different because they have different masses
how many isotopes do elements consist of more than one isotope
chlorine exist with mass number 35 and 37. Chlorine 35 contains 17p, 18n while Chlorine 37 contains 17p, 20n
The proportion of each isotope in a given element is called the relative abundance
The relative abundance the ratio or percentages in which they exist in the world.
If the relative abundance is minute and is insignificant then it is not considered in calculating the relative atomic mass for placement in the periodic table
although isotopes of elements exist, the relative atomic masses are whole numbers whereas there are some whose masses are not whole numbers.
The mass of an element depends on the relative abundance of the isotopes present in the element.
The actual mass of an atom is so small that it is not practical to work with therefore a reference is used and compared to the actual atomic mass
1961- it was agreed internationally that the carbon 12 isotope should be used as the reference
the mass of an atom relative to (compared to) the reference is called the relative atomic mass
The relative atomic mass the average weight and relative abundances of the isotopes of elements in naturally occurring samples are measured
the relative atomic mass is not usually a whole number because the mass of an atom compared to one twelfth the mass of a carbon 12 isotope.
the relative isotopic mass the mass of a single isotope compared to one twelfth the mass of a carbon 12 isotope
1919 F. Aston developed the mass spectrometer
the mass spectrometer is used to measure the mass an relative abundance of each isotope in a sample of naturally occurring element
main steps involved in the operating principles of the mass spectrometer 1. Ionization 2. Acceleration 3. Deflection 4. Detection
Acceleration The positive ions move into the accelerating chamber where an electric field accelerates positive ions towards a magnetic field.
deflection The fast moving ions are deflected according to their mass and charge as they pass through the magnetic field. Ions with lower mass to charge ratios are deflected more than ions with higher mass to charge ratios
the mass spectrum of chlorine atoms shows the relative abundance of chlorine-35 is 75.8% and chlorine-37 is 24.2%. calculate the relative atomic mass (Ar) of chlorine 35.5
1903 Henri Bacquerel was awarded the Nobel prize for physics for his discovery of radioactivity
marie received a second nobel prize in 1911 for chemistry for her isolation of radium. her research in radioactivity was immediately applied to the treatment of cancer and other diseases
what the Curie's discovered the radioactive elements radium and polonium
the force of attraction in the nucleus is a strong nuclear force of attraction that exists between nucleons. the nucleons are intimately involved in this attractive force
as the number of protons increases in the atom the positive charges in the nucleus repel each other so that the number of neutrons needed to create a stable nucleus increases more rapidly than the number of protons
even with an increasing number of neutrons to protons in the nucleus nuclei with 84 or more protons are unstable
unstable nuclei are called radioisotopes (radioactive isotopes)
unstable nuclei become stable by spontaneously ejecting alpha particles, beta particles and gamma radiation
the emission of alpha and beta particles changes the number of protons in the nucleus so that a different atom is produced
Alpha particles are helium nuclei
in nuclear reactions it is understood that alpha particles are formed without its electrons therefore the symbol "He" is used in nuclear equations
Emission of alpha particles leads to a decrease in atomic number by 2 and mass number by 4
eg of emission of alpha particles a
beta particles are formed when a neuron disintegrates giving a proton and an electron. the proton remains in the nucleus of the atom, so its atomic number increases by 1. the mass number is unchanged
eg of beta particles forming d
Gamma rays are electromagnetic waves of short wavelength
emissions of alpha or beta particles are often accompanied by the emission of gamma rays
Created by: 868TOYA
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