MCAT Atomic Theory and Composition Flashcards
What is matter?
Pure substances of a mixture.
Elements v. Compounds
Elements cannot be broken down into smaller parts whereas compounds can be broken down into constituent parts and has distinct chemical properties.
Atoms makes up elements and gives the distinct properties of that element.
Describe the components of atoms?
Neutrons - located in nucleus, contains a neutral ( no) charge.
Protons- located in nucleus, contains a positive charge.
Electrons - located in orbitals surrounding the nucleus, contains a negative charge.
Homogenous v. Heterogenous mixtures
Heterogenous - substances are different from each other.
Homogenous - substances are the same.
Atomic number v. Atomic mass
Atomic number represents that number of protons ( and the number of electrons if the atom neutral).
Atomic mass represents that number protons and neutrons and represents the mass of the atom.
Therefore we can find the number of neutrons by subtracting the atomic mass and atomic number.
Ions
When atoms contains unequal number of electrons.
Cations - lose electrons and has a + charge.
Anions - gain electrons and has a - charge.
Isotopes
Elements that has different number of neutrons, even though they contain different number of neutrons they have the same elemental identity.
Isotopes has the same chemical identity but different physical identity.
How do we measure the mass of isotopes
Via the atomic mass unit ( amu) which is the mass of of 1/12 of a carbon-12 atom.
The atomic mass ( or atomic weight) is the average weight of all of that element’s isotopes.
What’s the basis behind radioactive decay?
When the balancing forces between nucleons and electrons falls apart the nucleus can eject high energy particles or rays in an effort to establish equilibrium.
Alpha decay
Characterized with the ejection of an alpha particle.
4
2 He
- Alpha particle consists of 2 protons and 2 neutrons.
- We can a resulting atom with an atomic number that’s 4 less and an atomic number that’s 2 less.
Electron emission ( beta minus decay)
When a neutron is converted to a proton and an electron is expelled. This results in no change in the atomic mass but an increase in the atomic number.
Positron emission
Happens when a proton is converted to a neutron and a positron is emitted, results in a decrease in the atomic number but not the atomic mass.
Electron capture
Happens when a proton and electron are combined and turns into a neutron but no particles are released. This results in a decrease in atomic number but no change in atomic mass.
Gamma decay
A high energy gamma ray ( photon) is released, no change in atomic mass or atomic number.
How do we determine the half- life from a radioactive decay plot?
We identify the original amount at the top of the graph and see how long it takes for that amount to decrease by half.
Bohr model
Model that shows a proton with a single electron orbiting the proton in a single orbit.
The electrons in the orbit in discrete energy levels ( no in-between).
Energy levels of electrons further from the nucleus v. closer to the nucleus
Electrons further out from the nucleus has more energy than electrons closer to the nucleus.
What happens when electrons gain energy? When it loses energy?
When an electron moves to a higher energy orbital it gains energy from light ( photons) or heat.
When an electron moves from a higher energy orbital to a lower orbital it loses energy in form of light ( photons).
The energy released or absorbed is proportional to the difference in the energy of orbitals.
Electromagnetic radiation
Has waves and particle properties.
The energy is directionally proportional to the frequency. But frequency is the inverse of the wavelength.
Emission line spectrum v. Absorption line spectrum
Electrons are absorbed or emitted in specific energies creating line spectrums.
Excited state v. Ground state
Excited state is when an electron gains energy and move up to a higher energy orbital.
Ground state is when an electron releases energy and moves to a lower energy orbital.