A29 Matter to Atoms to Compounds - Democritus and Dalton [Unit 1]

matter def

this is anything that occupies space and has mass

elements def

these are each of more than one hundred substances that cannot be chemically interconverted (which means changing one element into another element or cannot break down into simpler substances. each element is distinguished by the number of protons in it's atoms. this number of protons is called the atomic number and can be found on the periodic table.

atom def

this is the smallest particle of matter that retains the chemical properties of the element to which it belongs. if the particle is different than an atom of any element it cannot be that element.

pure substances def

this is a sample of matter in which all of the particles are the same. there is only one substance present in a sample of a pure substance.

mixture def

this is a sample of matter in which all of the particles are not the same. there are two or more different substances present in a mixture.

molecule def

this is a particle that consists of two or more atoms that are bonded together. they can be two atoms of the same element or two or more atoms of different elements.

Who was the first individual to come up with the concept of atoms? When and where was he from? Was he a scientist? Did he ever test his idea?

Democruitus - Ancient Greece- 442 BC- No, he was a philosopher -No test

What did Democritus call atoms? How did he describe the concept? Did the original idea of atoms become popular and accepted quickly?

"Atomos" = invisible in greek. He stated all matter is made up of tiny indivisible particles. space between particles was a void. No.

Who's idea of matter contradicted the original idea of the atom? When and where was he from? Was he a scientist? Did he ever test his idea?

Aristotle - Ancient Greece - after Democritus - Not a scientist - No test

How did Aristotle who refuted the concept of atoms describe the make-up of matter? How long was this idea accepted by society?

He stated all matter consists of a mixture of four elements (earth, air, water, fire)

Who was the first scientist to complete experiments that provided scientific evidence that atoms existed? When and where was he from? What was his occupation?

John Dalton - 1803s - England - Scientist, teacher, preacher, meteorologist

what are the six postulates of Daltons atomic theory? (which ones remain true with current understanding of atoms?)

1. All matter is composed of extremely small particles called atoms. TRUE

2. Atoms of a given element are identical in size, mass, and other properties.

3. Atoms of different elements are different in size, mass, and other properties. TRUE

4. Atoms are indivisible and cannot be subdivided, created, or destroyed.

5. Atoms of different elements can combine in simple whole number ratios to form chemical compounds. TRUE

6. In a chemical reaction, atoms can be combined, separated, or rearranged. TRUE

why are certain postulates of Dalton's Atomic Theory no longer accepted with current understanding of atoms? explain why.

2. there are isotopes and ions of the same element with different mass

4. atoms have subatomic particles (protons, electrons, neutrons)

monatomic elements def

these are single atoms of a particular element (ex. S, Fe, Au)

diatomic elements def

these are molecules of two atoms of the same element bonded together (ex. H2, O2, N2, Cl2, Br2)

compounds def

these are substances that consist of atoms from two or more different elements that are combined in a specific whole number ratio

molecular compounds def

nm+nm. these are compounds that we call molecules that consist of two or more non-metal atoms that are bonded together (ex. CO2, C6H2O6, H2O, NH3, SO2)

ionic compounds def

m+nm. or NH4 ammonium which acts like a metal+nm. these are compounds that consist of positive metal cations and negative metal anions bonded together in large structures called crystal lattices. an ionic compound as a specific whole number ratio of each atom type. (ex. NaCl, CaCl2, LiF, NaNO3, K3PO4)

law of definite proportions def

a compound always contains exactly the same proportions of its elements by mass

what mathematical calculations can we use to show the mass properties of elements in a compound? and what formula is used to do this?

Percent Composition %Element = mass element/mass compound x 100 (total composition (by mass) added up of all the elements in a compound = ~100%

law of multiple proportions def

whenever the same two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.

ex of law of multiple proportions using carbon monoxide [CO] and carbon dioxide [CO2]

CO = mass O/mass C = 16g/12.01g = 1.33g

CO2 = mass O/mass C = 32g/12.01g = 2.66g

ratio of CO to CO2 = 1:2

why are the law of definite proportions and law of multiple proportions important?

Dalton used these formulas/laws to provide evidence to prove that atoms existed

law of conservation of mass def

during a chemical reaction, matter is neither created nor destroyed. the mass of the reactants is equal to the mass of the products in a chemical reaction. this is because all of the atoms that go into a chemical reaction as reactants must come out of the chemical as products.

3 H2 + N2 -->

2 NH3

4 Al + 3 O2 -->

2 Al2O3