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Structure of Atoms Physical Science Chapter 4 – Section 2.

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Presentation on theme: "Structure of Atoms Physical Science Chapter 4 – Section 2."— Presentation transcript:

1 Structure of Atoms Physical Science Chapter 4 – Section 2

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

3 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 )

4 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

5 Atomic Components Protons ( +1 charge / 1.67 x kg ) Neutrons ( 0 charge / 1.67 x kg ) Electrons ( -1 charge / 9.11 x 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

6 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 )

7 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?

8 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

9 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?

10 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

11 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 u, with 35 mass number – Most common Cl form contains 18 neutrons

12 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 x when put into scientific notation – 1 mol of marbles = x marbles – 1 mol of atoms = x atoms ( any atom ) – 1 mol of He atoms = x He atoms

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

14 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 g – Molar mass ( in g ) equals average atomic mass ( in u ) – Carbon-12 has u as well as g/mol Figure 7 in text

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

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


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