Chapter 4 Atomic Structure & Periodic Trends Flashcards
(20 cards)
What is the structure of an atom?
- Nucleus contains protons (+1 charge) and neutrons (no charge)
- Electrons (-1 charge) are held around the nucleus by electrostatic attraction of the positively charged nucleus.
What are atomic numbers and mass numbers?
- Atomic number (Z) = number of protons in an atom
- Mass number (A) = number of protons + number of neutrons
- While denoting these numbers with the element symbol, A is the number on the top left while Z is the number on the bottom left.
What are isotopes?
atoms of the same element that have a different number of neutrons, hence a different mass number (A).
What is the atomic weight of an element?
It is the weighted average of the masses of various isotopes of a particular element.
The formula includes atomic mass of an isotope and its abundance in nature.
What is radioactivity?
Unstable nuclei are called radioactivity
What are the two types of ions?
- cation = positively charged ion
- anion = negatively charged ion
What is radioactive decay?
Processes that help stabilize radioactive nuclei (parent). The stable nuclei formed are called the daughters.
- Types of radioactive decay - alpha, beta, gamma.
What is alpha decay?
Stabilization by reducing protons and neutrons
Radioactive nuclei stabilize themselves by emitting an alpha particle (2 protons, 2 neutrons).
What is beta decay?
Stabilization by adjusting the number of neutrons
- beta(-) decay = when an atom contains too many neutrons, it converts one neutron into one proton and one electron. The electron is emitted, but now the atom has a greater atomic number
- this is the most common type of beta decay.
- beta(+) decay = when an atom contains too few neutron, it converts one proton into one neutron and one positron. The positron is emitted, while the daughter now has a lower atomic number
- electron capture = when an atom uses an electron and a proton to make a neutron. Again, the atomic number is reduced by 1.
What is gamma decay?
after a radioactive atom undergoes either alpha or beta decay, it is in an excited state. To relax, atoms release gamma photons (no neutrons or protons).
What is the major difference between gamma decay and the two other?
- Gamma decay only releases energy, while alpha and beta decays both change the identity of the nucleus.
What is a half-life?
Half-life of a radioactive element is the time it takes for half of the sample to decay.
- formula: N = N(0)*(1/2)^(T/t(1/2))
N: mass of element at a given time
N(0): mass at time=0
T: total time
t(1/2): half-life
What is nuclear binding energy?
- The energy equivalent of
d(m) = mass of nucleons - mass of nucleus - 1 kg = 9e16 J
- 1 eV = 1.6e-19
- E(in eV) = d(m; amu)*931.5MeV
What is the formula for energy released by photons?
E(photon) = hf = h*c/lambda
What is the formula for calculating energy of a discrete energy level?
E(n) = (-2.178e-18)/(n^2)
What are the four quantum numbers?
- Shell (n) - n = 1, 2, 3, …
- Subshell - s, p, d, f,… every shell consists of one or more subshells where electrons are held
- Orbitals - each subshell consists of one or more orbitals; s contains 1; p contains 3, and so on
- Electron spin - each orbital can hold 2 electrons – one spin-up and the other spin-down.
What are the three rules for electron configuration?
- Aufbau - electrons occupy subshells in an order of increasing energy (s fills before p)
- Hund - electrons occupy orbitals singly before pairing up
- Pauli exclusion - no more than two electrons can occupy one orbital.
What are diamagnetic and paramagnetic atoms?
- electrons in diamagnetic atoms are all spin-paired; they are repelled by an external magnetic field
- electrons of a paramagnetic atom are not all spin-paired; they are attracted by an external magnetic field.
What are some anomalous electron configurations?
In the d block, d4 and d9 atoms achieve relative stability by moving one electron from the preceding s orbital to the d orbital. For example, 4s2 3d4 is more stable when written as 4s1 3d5.
