Unit 1 - Matter & Chemical Trends, and Chemical Bonding Flashcards
Matter
Matter consists of pure substances and mixtures
Pure Substances
Pure substances consist of elements (ex: oxygen) and compounds (ex: water)
Mixtures
Mixtures can be classified as:
- Homogeneous
- Heterogeneous
- Mixtures can be separeted into their components (pure substances), by physical means.
Compounds
in a compound, atoms are bounded chemically, therefore, they can only be separated into its constituent elements through a chemical reaction.
Homogeneous
Visibly indistinguishable components; also known as a solution; has uniform composition throughout.
Heterogeneous
Visibly distinguishable components
Distillation
Distillation is a process that depends on differences in the volality of the components; this method is ideal for separating a liquid from a solid in a homogeneous mixture. It is also a good methods for separating a homogeneous mixture of 2 liquids as long as their boiling points are not too close.
(Note: volality - the tendency of a substance to vaporize)
Filtration
Filtration is a method of separating a solid from a liquid in a heterogeneous mixture.
Chromatography
Chromatography is a separation method using a mobile phase and a stationary phase.
Paper Chromatography
A simple type of chromatography which uses a strip of porous paper, such as filter paper, as the stationary phase.
Where does the term “atom” come from? What does it mean?
Atom comes from the Greek word “atomos” meaning indivisible
Note: indivisible - unable to be divided or separated
Dalton’s Atomic Theory
-All matter is made up of small particles called atoms. An atom cannot be divided into smaller particles.
-The atoms of one element have the same properties, such as mass and size. These properties are different from the properties of the atoms of any other element.
-Atoms of different elements combine in specific proportions to form compounds. (Ex: 2 atoms of hydrogen combine with one atom of oxygen to form water; law of conservation of mass)
-In chemical reactions, atoms are not changes; rather, they are reorganized (Law of conservation of mass).
(Note: we now know that atoms can be broken down further into subatomic particles)
Thomson’s Atomic Model (The Plum Pudding Model)
He assumed that an atom consisted of a diffuse cloud of positive charge with the negative electrons embedded randomly in it.
Rutherford’s Atomic Model
He performed a series of experiments to test Thomson’s model. He reasoned that if Thomson was correct, the positive alpha particles should travel through the sheet with very minor deflections in their path. However, the results were different than he expected! Most of the alpha particles passed through as he anticipated, but many were deflected at large angles and some were reflected never hitting the detector. He reasoned that the large deflection of the alpha particles could only be caused by a center of concentrated positive charge that contains most of the atom’s mass.
Bohr’s Atomic Model
He stated that the electron in a hydrogen atom moves around the nucleus only in certain allowed circular orbits.
(Note: Quantum scientist indicated that although electrons do move in certain allowed regions around the nucleus called “energy levels”, the path is not circular. We can’t actually know the exact position of an electron at each instant while it is moving.)
Electron
Mass (kg): 9.109 x 10^-32
Relative Charge: -1
Relative Position: surrounding the nucleus
(Note: the number of electrons is the same as the number of protons for a neutral atom!!)
Proton
Mass (kg): 1.673 x 10^-27
Relative Charge: +1
Relative Position: nucleus
(Note: the number of protons determines the identity of the atom!!)
Neutron
Mass (kg): 1.675 x 10^-27
Relative Charge: 0
Relative Position: nucleus
Atomic Number (Z)
The number of protons in an atom, it is written as a subscript in the element symbol
Mass Number (A)
The total number of protons and neutrons in an atom, it is written as a superscript in the element symbol
Element Symbol
^AXZ
Note: where A is a superscript, Z is a subscript, and X is the element!
Isotopes
Atoms with the same number of protons but different number’s of neutrons
Group or Family
A vertical column in the periodic table is called a group or family
Period
A horizontal row is called a period
Alkali Metals
The elements of group 1A, with the exception of hydrogen
Note: the word “alkali” means “basic”, and these metals form basic compound upon reaction with water
Alkali Earth Metals
The elements of group 2A; they not only form basic compounds upon reaction with water, but they are also found in high abundance in the earth’s crust.
Halogens
The elements of group 7A
Note: the word “halogen” means “salt maker”
Noble Gases
The elements of group 8A; under normal conditions these elements exist as monoatomic gases.
(Note: monoatomic - consisting of one atom)
Atomic Size (Radius)
The distance from its nucleus to the approximate outer boundary of its electron cloud.
From top to bottom: atomic size increases
From left to right: atomic size decreases
Effective Nuclear Charge
The net force of nuclear attraction experienced by the valence electrons
Ionization Energy (IE)
Ionization energy is defined as the minimum energy required to remove the most loosely held electron from an atom or an ion at its gaseous, ground state. To ionize an atom means to remove an electron from it.
From top to bottom: decrease in magnitude of the IE
From left to right: IE increases
Electron Affinity (EA)
Electron affinity, EA, is defined as the energy change associated with the addition of an electron to an atom or an ion at is gaseous, ground state
From top to bottom: EA becomes more positive/less negative (Note: becomes less favourable to add an electron as the distance from the nucleus increases)
From left to right: EA becomes more negative/less positive (Note: becomes more favourable)
Electronegativity
The measure of the ability of an atom to attract electrons in a bond. Electronegativity values are based on a variety of properties such as ionization energy and electron affinity.
Bottom left to top right: electronegativity increases (Note: with exception of Nobel gases, 8A)
What is the most electronegative atom?
Fluorine
What is the least electronegative atom?
Francium and cesium
Covalent Bond (Non-Polar Covalent Bond)
When the electronegativity difference (ΔEN) between 2 atoms is zero or very small, a covalent bond is formed between them. This means that the electrons are shared equally by the 2 atoms.
Polar Covalent Bond
If the ΔEN is intermediate, the bond is polar covalent, in which case the shared electrons spend more time around the more electronegative atom. The more electronegative atom pulls he shared electron cloud more towards itself.
(Note: since the electron density is greater around the more electronegative atom, it is said to have a partial negative charge (δ-), and the less electronegative has a partial positive charge (δ+).)
Ionic Bond
In general, when the ΔEN between 2 atoms is large, an ionic bond is formed between them. In the formation of an ionic bond, one or more valence electrons are completely transferred from the less electronegative atom (metal) to the more electronegative atom non-metal) producing positive and negative ions. The electrostatic force of attraction between oppositely charged ions is what we call ionic bond.
Cation
When an atom loses one or more electrons, a positive ion, or a cation is formed
Anion
When an atom gains one or more electrons, a negative ion, or a anion is formed
Atomic Mass
The atomic mass of an element is a weighted average of the masses of the isotopes of that element.
Average Atomic Mass
The average atomic mass of an element is usually called the atomic mass of that element for simplicity
Main Group Elements (Representative Elements)
Known as A block elements
Groups: 1,2,13-18
Transition Metals
Known as B block elements
Groups: 3-12
Inner Transition Metals (Rare Earth Metals)
Lanthanides and Actinides
Periodic Trends: Why should the element be in the gaseous state?
When an element is in the gaseous state, the atoms are far apart from each other, and there is no force of attraction between them. This means that an electron in an atom is only attracted by the nucleus of that atom, and is not influenced by the nuclei of the surrounding atoms.
Periodic Trends: Why should the element be in the ground state?
The ground state (or the relaxed state) or an atom is the state at which the electrons of the atom are where they should be. When they are given sufficient energy, they jump to higher energy levels; electrons are said to be in “excited” states. We want all atoms to be at there ground states when we begin to use energy to ionize them so that we can have the same reference point for comparison purposes.
What is a chemical bond?
A chemical bond is a strong attractive force between 2 atoms in a molecule of between 2 ions. We can predict the type of bond that can be formed between 2 atoms based on their affinities for electrons.
