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Atoms, molecules, and ions

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Sarah Rodney

on 8 September 2016

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Transcript of Atoms, molecules, and ions

Ionic - form crystals to maximize the interactions between cations and anions - crystal packing or stacking pattern
Covalent - less frequently are crystals
Silicone and sucrose - crystals
Rubber and wood - not crystals
matter can be neither created nor destroyed

because matter is made of atoms that are unchanged in a chemical reaction following that mass must be conserved as well

Convinced with lab?
Atoms, molecules, and ions
The History
Atomic number, mass number, and isotopes
The periodic table...we meet again!
Dmitri Mendeleev and Lothar Meyer - In 1869 elements arranged according to atomic masses certain properties repeat at regular intervals. So first periodic tables! Some blank spaces...oh well ;-p
50 years later found out that the correct ordering property was the atomic number, Z
Dimitri Mendeleev - blank spaces must be undiscovered elements so he predicted the properties
Molecules and ions
Monatomic - 6 noble gases that only exist as single atoms in nature (He, Ne, Ar, Kr, Xe, and Rn)
monatomic ions
Molecules - an aggregate of at least 2atoms in a definite arrangement held together by chemical forces (bonds)
Diatomic molecule - contains only two atoms H2, O2, I2, Br2, Cl2, N2, F2, HCl, CO
Polyatomic molecules - molecules containing more than two atoms. H2O, O3, NH3
Chemical formulas
Expressing composition of molecules and ionic compounds in terms of chemical symbols
Atomic Theory
5th century B.C. Democritus expressed belief in invisible particles (atomos)
1808 - John Dalton....and more! To the video because we have done enough work for today.
Structure of the Atom
atom - basic unit of an element that can enter into a chemical combination
Subatomic particles - electrons, protons, neutrons
The Electron
1890's radiation was the thing - emission and transmission of energy through space in the form of waves
Cathode ray tube - J.J. Thomson
cathode ray drawn to positive charged plate (anode) - electrons
Plum-pudding model
X-rays - Wilhelm Rontgen
energetic radiation penetrated matter, darkened covered photographic plates and some substances to fluoresce - not effected by magnet so no charge
Radioactivity - Antoine Becquerel and marie Curie
spontaneous emission of particles and/or radiation
Protons and nucleus
Ernst Rutherford - New Zealand
Alpha particles to probe structure - gold foil experiemnt finding nucleus
With Hans Geiger and Ernst Marsden
1pm = 1x10^-12m
Atomic radius = 100pm
Atomic nucleus 5x10^-3 pm
Marble in a stadium
The neutron
James Chadwick (1932) - bombarded sheet of beryllium with alpha particles where he found evidence of the neutron
Neutron = 1.67493x10^-24 g
Proton = 1.67262x10^-24 g
Electron = 9.10938x10^-28 g
Naming Molecular Compounds
Intro to Organic compounds
Hydrocarbons - compounds with only hydrogen and carbon
Dalton's atomic theory - 1808
1. elements are composed of extremely small particles called atoms
2. all atoms of a given element are identical with the same size, mass, and chemical properties. Atoms of one element is different from another.
3. Compounds are composed of atoms of more than one element. The ratio of the numbers of atoms of any two elements present is either an integer or a simple fraction.
4. Chemical reactions are just separations, combinations, or rearrangements of atoms; no creation or destruction of atoms.
Joseph Proust's Law of definite proportions - 1799 (French chemist)
"Different samples of the same compound always contain its constituent elements in the same proportion by mass"
Dalton's law of multiple proportions
If two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers.
Dalton's law of conservation of mass
R.A. Millikan
Proved the charge on each electron was the same - oil drop experiment
Used electrostatics to find mass of an electron to be 9.10x10^-28g
Three types of radiation
Alpha, Beta, and Gamma
Ion - atom or group of atoms that has a net positive or negative charge
Cation -ions with net +charge
Anion-ions with net -charge
Ionic compound - formed from cations and anions (ionic bond)
Monatomic ions - ions with only one atom, Mg+2, S2-, Na+, Cl-
Polyatomic ions - ions containing more than one atom
Molecular Formulas
Shows the exact number of atoms of each element in the smallest unit of a substance
No subscript means there's only one of the elements
Allotrope - one of two or more distinct forms of an element - carbon - diamond or graphite
Molecular models
Ball-and -stick models and space-filling models
Structural formula- shows how atoms are bonded together in a molecule
Empirical Formula
Tells us which elements are present and the simplest whole-number ratio of their atoms. NOT NECESSARILY THE ACTUAL NUMBER of atoms in a given molecule.
Simplest chemical formula
Rocket fuel! N2H4 what is the empirical formula?
Used to determine unknown samples and then additional experiments to find the actual ratio
Empirical formula for chloroform?
Formula of Ionic Compounds
Three-dimensional arrangement - basic ratio is called a Formula Unit
Ionic bond - giving and taking of electrons
Want to make the compound neutral by balancing out the cations and anions
Subscript of the cation is numerically equal to the charge on the anion, and the subscript of the anion is numerically equal to the charge on the cation
Formulas of ionic compounds are usually empirical formulas
Try potassium bromide, Zinc iodide, and Aluminum oxide
Naming Compounds
People used to name compounds from how they looked, properties, and applications
There are too many so we had to make a system
Organic compounds - contain carbon...usually in combination with hydrogen, oxygen, nitrogen, and sulfur
Inorganic compounds - ...everything else. There are some exceptions. CO, CO2, and CS2. We will talk about these later.
Categories of inorganic compounds Ionic compounds, molecular compounds, acids and bases, and hydrates.
Naming ionic compounds
Usually alkali and alkali earth metals and nonmetals
Exception is Ammonium ion = NH4+
many binary compounds(just two elements)
First element is named followed by the nonmetallic anion - NaCl
Chlorine and added "-ide"
ionic compd cont.
"-ide" ending also used for certain anion polyatomic groups
hydroxide (OH-), cyanide (CN-) = ternary compounds - contains three elements
Certain metals (mainly transition metals) form more than one type of cation
"-ous" fewer positive charges and "-ic"more positive charges
Stock system - roman numerals
manganese(II) oxide MnO2
name these: SiCl4, P4O10, NF3, Cl2O7
Naming Acids and Bases
Acid - substance that yields hydrogen ions(H+) when dissolved in water
Anions that end in "-ide" form acids with a "hydro-" prefix and "-ic" ending - hydrochloric acid or hydrogen chloride?
Oxoacids - containing H, O, and another element = Written H first, element, and then O
Remove H's from "-ic" acid ends with "-ate"
Removed from "-ous" becomes "-ite"
If not all H's removed must indicate with prefixes.
Naming Bases
Base = a substance that yields hydroxide ions (OH-) when dissolved in water
Ammonia (NH3) is a common base
Hydrates = compounds that have a specific number of water molecules attached to them
Anhydrous = no waters attached
Ionic and Covalent Compound Characteristics
Electronegativity - measure of how much an element wants to pull electrons away from an element it has bonded to
Dissimilar electronegativity - ionic (vegan and meat)
Similar electronegativities - covalent (2meatatarians)
Melting and boiling points
Ionic compounds - high
Covalent - low
Not set in stone
Usually if something melts after less than 30seconds over bunsen burner, then it indicates a covalent compound
Electrical Conductivity when dissolved in water
Ionic - conduct (not when solid so depends on solubility in water ex. CaOH)
Covalent - never conduct
Because cations and anions can move around easily and the motion of ions cause electricity to be conducted through the liquid
Ionic compounds rarely burn
Decompose at high temps
Covalent compounds burn and tend to be flammable
Some exceptions - CH2Cl2 and CO2 don't burn
Ionic - hard and brittle (almost without exception)
Strong electrostatic reactions between ions in ionic crystals
Covalent - frequently held together by intermolecular forces (dipole-dipole forces or hydrogen bonds)
Not as hard as ionic and dislocations don't cause the entire structure to disintegrate
Of course there are some exceptions (sugar)
Metals - good conductors of heat and electricity, malleable, ductile
Nonmetals - poor conductors of heat and electricity, gain electrons
Metalloids - mixed properties, semiconductors because of their intermediate (and highly temperature dependent) electrical conductivity
Atomic number (Z) - number of protons in the nucleus of each atom of an element
Mass number (A) - the toal number of neutrons and protons present in the nucleus of an atom of an element (atomic mass)
Mass# = # protons + # neutrons = atomic # +#neutrons
Isotopes - atoms that have the same atomic number but different mass numbers (isotopic mass and isotopic abundance)
Deuterium - hydrogen with 1proton and 1neutron
Average Atomic mass - weighted average mass of an atom of an element based on the relative natural abundance of that element's isotopes
Covalent bond: sharing of electrons
Usually two nonmentals
Binary comounds = same as ionic naming
Use prefixes when naming two nonmetals on the right of the periodic table
"mono-" can be omitted if first
In oxides "a" ending sometimes omitted - N2O4
Determining Electronegativity
Pauling electronegativity scale - this uses electron volts and hydrogen as the reference (2.20)
Take difference of electronegativities (DEN)
0.0 - 0.4 = nonpolar covalent
0.5 - 1.7 = polar covalent
greater than 1.8 = Ionic
Check electronegativity chart
Polarity Arrow
Positive side of arrow is the least electronegative atom
Pointing where electrons want to move
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