Chapter 4 Atomic Structure

___________ means indivisible, from Democritus (Greek, 400BC) smallest particle of an element that retains the chemical properties of that element ____________: transformation of substances into one or more new substances Up to late 1700’s, info about reactions were qualitative Technology improved scales/balances so that quantitative analysis would be more accurate.

Dalton’s Atomic Theory In ______, John Dalton transformed Democritus' ideas into scientific theory

1)All ________ is composed of tiny indivisible particles called atoms 2)Atoms of the same __________ are identical – size, mass, etc… Atoms of different elements are different. 3) Atoms of different elements combine in simple whole-number ratios to form _________________ 4) In chemical reactions, _______________________, separated or rearranged. (but not created, destroyed or transformed) Dalton’s Atomic Theory

Modern Atomic Theory Dalton thought atom was solid & indivisible There are 3 major differences between Dalton’s and the Modern theory 1)Atoms are made up of ___________________ – protons, neutrons & electrons 2)Atoms can be changed from one element into another – by __________ reaction 3)Atoms of the same element are not all exactly the same - ___________

Structure of the Atom Atom: smallest particle of an element that retains the _____________________ of that element Although teeny tiny, the atom can be seen using a scanning tunneling microscope. Once we can see it, we can manipulate it There is an emerging branch of chemistry… ___________________ that is concerned with those things that are very small… like microchips etc

Structure of an Atom Atom consists of ___________________ – that occupy the small nucleus and the larger surrounding area _________ at the center of the atom contains ________ (positively charged) and ________ _____________ (negatively charged) occupy a region surrounding the nucleus … but how did we discover these things?

Discovering the Electron Late 1800’s, experiments were carried out on Cathode Ray tubes – basic research to see what would happen if electric current passed through a gas at low Pressure producing ______________________

J.J. Thomson (English guy) used this device to calculate the ratio of charge of these cathode ray particles to their mass, which he found to be negatively charged and constant These cathode ray particles are now known as ________________________

1909: Robert Millikan (American physicist) showed that mass of electron ~ 1/2000 mass of Hydrogen atom (its actually 1/1837 th ) Millikan’s experiments confirmed that _______________________ _______________________ _______________________ _______________________

More Conclusions from Millikan 1)_______________, therefore, there must be a positive charge to balance the negative electrons 2)Electrons are a small % of the atom’s mass, therefore there must be _______ ______that make up most of the atom’s mass

Protons Since atoms are neutral, atoms must contain positive charge as well. Thompson believed that the atom was a cloud of positive charge with negative electrons embedded into it. This is known as the ________________________.

The Nuclues In 1911, Ernest Rutherford did an experiment where he bombarded a thin Gold foil with ______ _______– small, positively charged particles

They believed the _______________________ evenly distributed Rutherford, along with Geiger & Marsden, expected the alpha particles to simply go straight through, like a small ball bearing through a thin veil, but some were actually deflected back

Rutherford concluded that the atom consisted of a very small, dense centre that is positively charged, which he called the _____________ Also, that the nucleus was surrounded by a very large empty region in which the electrons occupied, like planets around the sun

Later, it was calculated that mass of a proton is ___________________________of an electron, even though they have equal but opposite charge

The Neutron The __________ is just slightly heavier that a proton but is neutral All atoms, except ____________, contain neutrons An atom is neutral when it contains equal numbers of protons and electrons i.e. # protons = # electrons It is solely the _____________that determine what type of element the atom is Protons, which are positively charged, can stay close to each other in the nucleus because of _______________

Some Facts… Particle SymbolCharge Mass(kg) Relative Mass __________e x __________p x __________n o x Size of atom is measured in picometres (pm) = m

Counting Atoms _____________(Z): of an element is the number of protons in the nucleus of each atom e.g. every Carbon atom has 6 protons (and also 6 e - ) The Periodic Table is arranged in order of ____________________________ The Atomic Number identifies the element (look at Periodic Table at back of book)

Isotopes: are atoms of the _____________________________different masses. Because all atoms of the same element must have the same number of protons (and electrons), they can only differ in the number of neutrons, which do not change the atoms identity

EXAMPLE: Hydrogen consists of just 1 proton & 1 electron and is also known as __________ There is another kind of Hydrogen that consists of 1 proton, 1 electron & 1 neutron, called _________ which is only 0.015% of all Hydrogen There is still another type of Hydrogen which has 1 proton, 1 electron & 2 neutrons, called _________

_________________(A): is the total number of protons & neutrons in the nucleus of an atom So, for Hydrogen: Name Atomic #(Z)Mass #(A) # protons # neutrons protons+neutrons Protium1 0 1 Deuterium1 1 2 Tritium1 2 3 So,# Neutrons = Mass #(A) – Atomic #(Z)

__________: general term for any isotope of any element Isotope/NuclideSymbolp + e - n o Protium 1 1 H110 Deuterium 2 1 H111 Tritium 3 1 H112

Atomic Masses Mass (not weight) of atoms is very, very small, i.e. around ____________ Better to use a relative scale to compare mass of atoms to each other, but you need a standard. Choose ______, which has 6 protons & 6 neutrons, 12 6 C, also known as ______________ It has been assigned a mass of exactly _________________units (amu) So: _________= 1/12 mass of Carbon-12 = x kg All other atoms are determined using this relative scale.

______________________: is the weighted average of the atomic masses of the naturally occurring isotopes of an element

Example from book: Copper -________ of all Copper is Copper-63 ( Cu) which has a mass of amu -________ of all Copper is Copper-65 ( Cu) which has a mass of amu Calculate Average Atomic Mass (_______ x amu) + (______ x amu)= amu = amu (2DP) (Revise Z#, A#, Atomic Mass & Average Atomic Mass)

Suppose you have: 10 pens (20%) “weighing” ½ oz each, and 40 pens (80%) “weighing” ¾ oz each. What is the average mass of each pen? Or, another way: (20% x ½ oz) + (80% x ¾ oz) =(0.2 x ½ oz) + (0.8 x ¾ oz) = 0.7 oz