Anything that has mass and occupies space exists as a solid, liquid, or gas.
How do you change from one state to another? The state of matter depends on temperature (heat energy)
Different terms to describe changes of state:
To understand how substances differ, you need to observe their properties
All matter has two types of properties:
- shine (luster)
- melting temp, freezing temp, boiling temp
- Determines the way a material behaves in a chemical reactions
- Ex. reaction to oxygen, acids, heat, water, ability to burn.
- When a substance undergoes a physical change, its state may be altered, but its chemical composition is the same ex. Ice cream melting!
- A chemical change is when 2 or more substances react and form 1 or more new substances ex. H₂ + O₂ forms H₂O
Is made of only 1 kind of matter and has a unique set of properties
- A pure substance is further classified into an element or a compound
Matter than cannot be broken down into any simpler substance.
- The most purest matter because it contains only one kind of atom
- Represented by a symbol of a capital letter, or a capital letter with lower case letters.
A substance formed by 2 or more elements chemically fixed in proportion.
A mixture is 2 or more substances physically (not chemically) combined
4 main types of mixtures:
Some or all particles can be seen and be separated (Ex. Salad)
Not separate visibly, as one is dissolved in another (Ex. coffee)
A substance dissolved in water is called an aqueous solution
Mixture where tiny particles of one substance are held within another. Substances can be separated by centrifuging or filtration. (Ex. Salad dressing)
Cloudy mixture, where the particles are suspended and difficult to separate (Ex. milk)
Observing Changes in Matter
When a substance undergoes a physical change, its state may be altered, but its chemical composition is the same
- To identify a physical change:
- You can separate the end products (reactants) to form the products again. Ex. Salt water, sand & rocks
- You are able to re-freeze or melt the product again. Ex. Ice cream, plastic mould
A chemical change is when 2 or more substances react and form 1 or more new substances
- The new substances formed are completely different from the original reactants
- To identify a chemical change:
- Change in color
- Change of odor (if present)…safety!!
- Formation of a solid (precipitate) or a gas
- Release or absorption of energy in the form of light & heat
Controlling Changes of Matter for Human Consumption
Freeze drying of food
- Steps in Preparation:
- 1. Food is frozen to ice (physical change)
- 2. Frozen food placed in pressure chamber to sublime ice (s à g) (physical change). Water gas is removed.
- 3. To eat food, stir in hot water
- Steps in Preparation:
Evolving Theories of Matter
Stone Age Chemists
Lived before 8000 B.C. in Middle East. Metal not discovered, used ‘stone’ tools. Learnt how to start, control, and use fire for cooking, glass, ceramics, bricks.
6000 BC to 1000BC - Chemists only worked with metals of high value to humans. Gold was popular due to its properties. Early human civilizations commonly used seven metals:
- Gold (Au) 6000 B.C.
- Copper (Cu) 4200 B.C.
- Silver (Ag) 4000 B.C.
- Lead (Pb) 3500 B.C.
- Tin (Sn) 2750 B.C.
- Iron (Fe) 1500 B.C.
- Mercury (Hg) 750 B.C.
- 1200 BC - Hittites learned how to extract iron from rocks …Iron Age begins! Iron + Carbon a steel (Very hard material for armor, weapons, tools)
- Metals not the only thing important, liquids too! Many cultures used juices and oils in everyday life and rituals
- 2500 BC - Greek philosophers realized that rock can be broken down into small pieces and into powder. Ie: Matter is made up of particles
- 400 BC - Democritus stated that each type of material was made up of a different type of ‘atomos’ which means indivisible. These different particles gave each material its own unique set of properties. By mixing different atomos, you could make new materials with their own unique properties.
- 350 BC - Aristotle stated that everything was made of earth, air, fire, and water.
- Because Aristotle was well known and well respected, his description of matter was preferred over Democritus’s description until 1600 AD.
From Alchemy to Chemistry
- 350 BC - 1600 AD- numerous alchemists (Arabic for ‘alkimiya’- “the chemist.”) practiced their pseudo-science (magic & simple experiments) trying to change metals into gold. They were not interested in understanding the nature of matter. Alchemists contributed useful lab tools from their practice. Ex. Beakers, filters, flasks, plaster of paris
- In 1597, the German alchemist Andreas Libau published ‘Alchemia’, a book describing the achievements of alchemists and how to prepare chemicals
New Interest in Atoms
- 1500s on- scientists had a greater interest in understanding the nature of matter and change. Based their theories on observations and experimentation rather than guesses and assumptions.
- 1600s Robert Boyle experimented with gases and came up with proof supporting 400 BC Democritus’ tiny particle theory. Boyle believed matter was composed of tiny particles with various shapes and sizes that grouped together to form other individual substances. He wanted to determine what each type of particle was.
- 1770’s- Antoine Lavoisier (French scientist) studied chemical interactions and naming the elements: hydrogen, oxygen, and carbon. Developed a system for naming chemicals that all scientists could use the same words. He was given the title of ‘Father of Modern Chemistry’
- 1808- John Dalton (English scientist and teacher)- suggested matter was made up of elements that are pure substances that contain no other substances. He put forward the first modern theory of atomic structure:
- 1) Each element is composed of a particle called an atom
- 2) All atoms of a specific element have identical masses
- 3) Different elements have different atoms of different masses
- He developed the ‘Billiard Ball Model’ where atoms are solid spheres. Theory held true until the discovery of electrons in 1897.
- 1897- J.J. Thompson (British physicist), discovered negatively charged sub-atomic particles electrons. Proposed the Raisin bun model of the atom. Atom is a positive center with negative electrons embedded in it like raisins in a bun. Electrons balance protons therefore atom has no electrical charge
• Theory held true until discovery of electrons were outside the nucleus.
Chemistry in the Modern Age
- 1904 - Hantara Nagaoka (Japanese physicist)- proposed an atomic model that resembled a mini solar system- planetary model. Center had a large positive charge and negative electrons circled the positive center like planets orbiting the sun
- Many did not agree with this model as they couldn’t explain it. The model existed until scientists realized a) nucleus is not massive b) electrons not closely connected to the nucleus
- 1907 - Ernest Rutherford (British scientist)- worked at McGill won the Nobel Prize for work in radioactivity. Supported Nagaoka’s model but modified it saying electrons float around randomly.
- His model suggest that atoms were empty spaces which positive particles could pass through with a positive central core (he called it a nucleus).
- Calculated the nucleus to be 1/10000 size of an atom. Like comparing a small green pea in a football field!
- Rutherford’s Discovery Was a huge contribution to atomic theory
- 1913 - Niels Bohr, Nobel Physics Prize, subjected that electrons move in a specific circular orbits (electron shells) and they jumped between shells by gaining or losing energy
- Late 1920’s- James Chadwick (British Physicist) discovered the nucleus contains protons (+ charge) and neutrons (no charge). Protons and neutrons have same masses. Electrons has a mass of 1/1837 of either a proton or neutron
- Early 1930’s- Quantum Theory explains existing in a charged cloud around the nucleus. Deals with probability chances of finding an electron in a specific area of the atom.
- All matter is composed of atoms with a positive nucleus containing protons and neutrons surrounded by negative electrons in a surrounding ‘cloud’; atoms may combine to form molecules.
Organizing the Elements
Early chemists looked for ‘patterns and property similarities’ between elements
- Early 1800’s, Dalton developed symbols for the elements known at that time
- 1814 - Jons Berzelius (Swedish chemist) used the first letter (capitalized) of the element name as the symbol ( Ex. Hydrogen = H). If there were more than two elements starting with the same alphabetical letter- use a small second letter behind the capital (Ex. Helium = He)
The average mass of one atom of an element compared to a standard Carbon atom at 12 amu’s (atomic mass units). This is the old definition of atomic mass, (now referred as amu). One could now list atoms in order of increasing atomic mass! Atomic mass is now defined the weight of P, E, N
1864 - John Newlands (English chemist)- recognized a pattern when elements were listed by increasing atomic mass I.e. element’s properties repeat themselves at regular intervals
1869 - Dmitri Mendeleev (Russian chemist & card player)- organized elements according to patterns in the properties of the elements. He showed that properties of elements vary periodically with increasing atomic masses. His chart had ‘gaps’ for future elements to be discovered that had properties and atomic masses to fit those gaps. He did this without even knowing what an atom was made of!
The Periodic Table
The Periodic Table…Past and Present
Mendeleev’s periodic table had 63 elements. Since then, many more elements have been discovered. Mendeleev’s table also had holes in it…to help place a spot when new elements were discovered. These holes were placed based upon the patterns noticed.
Today, a Periodic Table has around 112 elements. Some of these elements are very unstable and discovered using closed laboratory conditions
The Periodic Law
All the elements of the periodic table are arranged in a logical sequence. This sequence is the addition of one proton to each successive element. This arranges all the elements in order of increasing atomic weight. This method also arranges the elements according to similar properties (groups).
How Today’s Periodic Table Is Organized
- It is a series of boxes in rows and columns
- Period- 7 horizontal rows
- Group (family)- 18 vertical columns. Each Family has similar chemical properties
- Each element box contains:
Number above the symbol. Indicates # of protons or electrons in an electrically neutral atom. Atomic Numbers increase by one from left to right within the ‘periods’
Number below the name. Total mass of all protons and neutrons in the nucleus Ie. Average mass of element’s atoms
Atomic mass measured in amu’s - atomic mass units where one amu = 1/12 mass of a carbon-12 atom. Each has a mass of 1 amu.
Calculating the Number of Neutrons
1. Round off the atomic mass to the nearest whole number.
2. Subtract the atomic number from the atomic mass.
Eg. Magnesium (Mg)
Atomic mass = 24.1 ~ 24
Atomic number = 12
24 – 12 = 12 n /atom
Drawing a Sodium Atom in the Quantum Theory
1. Determine PEN.
2. Place P & N in nucleus.
3. Place electrons outside nucleus (2 e-, 8 e-, 8 e-, 18 e- )
General Patterns of the Periodic Table: physical properties
Metals: shiny, malleable, ductile, conduct electricity
- Found on the left side over to the right past middle (Lithium 3 to Polonium 84)
Metalloids or Transition elements: have both metallic and non-metallic properties
- Found between metals and non-metals
Non metals: solid (dull & brittle) or gases, don’t conduct electricity (insulators)
- On far right- Carbon 6 to Radon 86
Groups: 18 vertical columns referred to by the first element in the column
- All elements in group columns have similar appearance & properties
Periods: 7 horizontal rows. Left metals to right non-metals ex. Period 4 K (metal) to Kr (non-metal)
- Left side is more chemically reactive than the right side, which is less chemically reactive
Group 1 Elements: (not including H) are ‘alkali metals’, most chemically reactive with air or water. Reactivity increases as you go down the group
Group 2 Elements: ‘alkaline-earth metals’ also react with air or water, but not as vigorously as group 1
Group 17 : “Halogens’ most reactive non-metals. Fl, Cl, Br all react readily with Group 1 elements to produce useful compounds…like salt!
Group 18 : ‘ Noble gases’- very stable and unreactive. These gases combine with other elements under specialized lab techniques