Physical Science Chapter 4 – Section 2 Structure of Atoms Physical Science Chapter 4 – Section 2

State Standards CLE.3202.1.2 – Describe the structure and arrangement of atomic particles

What is an Atom? The three main components of an atom are distinquished by mass, charge, and location The chemistry of each element depends directly on these three components Nucleus: Protons ( positively charged ) Neutrons ( neutral – NO CHARGE ) Electrons ( negatively charged )

Electric Forces in Atoms Protons and electrons attract each other Electric force holds components together; the same forces hold solids and liquids together Liquid water is held together by electric forces

Atomic Components Protons ( +1 charge / 1.67 x 10-27 kg ) Neutrons ( 0 charge / 1.67 x 10-27 kg ) Electrons ( -1 charge / 9.11 x 10-31 kg ) All ( most ) elements contain all three Atoms of the same element contain the same number of protons, but neutrons may vary Each element has a unique number of protons

Distinguishing Elements and Atoms Atomic number – number of protons in an atom Mass number – number of protons & neutrons Isotopes – exist for an element if different atoms ( with the same atomic number ) have varying numbers of protons ( different mass numbers )

Hydrogen & Helium Hydrogen ( H ) contains 1 electron, 1 proton, and 0 neutrons [ Protium isotope ] Helium ( He ) contains 2 electrons, 2 protons, and 2 neutrons What is atomic number, mass number of H, He?

Isotopes of Hydrogen Protium – Most common form on Earth and Sun 1 electron, 1 proton, 0 neutrons Deuterium – small fraction of hydrogen; 1 out of every 6,000 hydrogen atoms in Earth’s crust 1 electron, 1 proton, 1 neutron Trillium – very unstable and so very rare 1 electron, 1 proton, 2 neutrons

Isotopes of Chlorine The common form of chlorine ( Cl ) has 17 protons, 17 electrons, and 18 neutrons Another form has 20 neutrons Neutrons can be calculated by using these How do we know which form is most common?

Atomic Mass Units Used to express the mass of such tiny particles Unified Atomic Mass Unit is 1/12 the mass of a Carbon-12 Carbon-12 isotope has a fairly even mass number 6 protons and 6 neutrons Remember electrons contribute little mass to atom Each proton/neutron has mass of 1.0 u Units given as a u

Atomic Mass Units The value of AVERAGE ATOMIC MASS found in the periodic table tells us which isotope of any element is most common ( HYDROGEN ) weighted average so most common form counts most Zinc with average atomic mass 65.4 u 65 ( closest mass # ) – 30 ( atomic # ) = 35 neutrons Most common Zn isotope has 35 neutrons Cl has average of 35.453 u , with 35 mass number Most common Cl form contains 18 neutrons

The Mole In order to count large numbers of small particles, a COUNTING UNIT was devised – THE MOLE ( mol ) Examples ( Avogadro’s number ): 1 mol = 602,213,670,000,000,000,000,000 particles Equals 6.022 x 1023 when put into scientific notation 1 mol of marbles = 6.022 x 1023 marbles 1 mol of atoms = 6.022 x 1023 atoms ( any atom ) 1 mol of He atoms = 6.022 x 1023 He atoms

The Mole How many stars in the universe? 2003, roughly 7 x 1022 stars counted ( within range Value could increase in future 6.022 x 1023 popcorn kernels would cover the USA in a pile 500 km ( or 310 mi ) tall!! Avogadro’s number is used only for small particles

Relating Moles and Grams Mass of 1 mol random atoms difficult to find Each element has a unique MOLAR MASS The mass of 1 mol of this type of atom ( element ) Usually accounts for several isotopes Mass of 1 mol of the same atom easy to find For Carbon-12, molar mass is 12.00 g Molar mass ( in g ) equals average atomic mass ( in u ) Carbon-12 has 12.01 u as well as 12.01 g/mol Figure 7 in text

Relating Moles and Grams Mass of 1 mol Carbon-12 atoms is 12.01 g USE PERIODIC TABLE 24 g Carbon-12 = 2 mol Carbon-12 3 mol Carbon-12 = 36 g Carbon-12

Molar Mass of Compounds, Molecules As elements ( atoms with same atomic number ) have a MOLAR MASS, so do coumpounds H2O : 2 Hydrogen with 1.00 g/mol & 1 Oxygen with 16 g/mol Gives ( 2.00 + 16 ) g/mol = 18 g/mol CO2 : 1 Carbon with 12.01 g/mol & 2 Oxygens with 16 g/mol Gives ( 12.01 + 32 ) g/mol = 44 g/mol O2 : 2 Oxygen atoms at 16 g each Gives: 32 g/mol for O2 molecules H O