Understand the experimental design and conclusions used in the ATOMIC STRUCTURE TEKS   Understand the experimental design and conclusions used in the development of modern atomic theory, including Dalton's Postulates, Thomson's discovery of electron properties, Rutherford's nuclear atom, and Bohr's nuclear atom. (TEKS 6A) (CCRS VII B-1) Use isotopic composition to calculate average atomic mass of an element. (TEKS 6D) (CCRS II B-1) Research and describe the history of chemistry and contributions of scientists. (TEKS 3F) Demonstrate safe practices during laboratory and field investigations. (TEKS 1A) (CCRS I C-3) [Concept Recommendations] Atomic Theories. [Rutherford, Thomson] Structure of the atom. (not electron configuration) Isotopes and Average Atomic Mass Charges Introduce Ions ATOMIC STRUCTURE   Understand the experimental design and conclusions used in the development of modern atomic theory, including Dalton's Postulates, Thomson's discovery of electron properties, Rutherford's nuclear atom, and Bohr's nuclear atom. (TEKS 6A) (CCRS VII B-1) Use isotopic composition to calculate average atomic mass of an element. (TEKS 6D) (CCRS II B-1) Research and describe the history of chemistry and contributions of scientists. (TEKS 3F) Demonstrate safe practices during laboratory and field investigations. (TEKS 1A) (CCRS I C-3) [Concept Recommendations] Atomic Theories. [Rutherford, Thomson] Structure of the atom. (not electron configuration) Isotopes and Average Atomic Mass Charges Introduce Ions

A World of Particles

indicates that an explanation is supported by overwhelming evidence. A model is a simplified representation of something you want to explain (so a model that represents the structure of an atom is called an atomic model). A “theory” indicates that an explanation is supported by overwhelming evidence. An Atom- the smallest unit of an element that retains the chemical properties of that element and can exist as a separate particle.

Atomic theory: All matter is made up of atoms, and helps us make accurate predictions about the behavior of matter.

Models of the Atom Solid Sphere Model ~460 BCE: Democritus And scientists that led us there! ~460 BCE: Democritus His question: Democritus wondered how many times it would be possible to break a piece of matter in half, if the pieces would just keep getting smaller forever. He thought that if he could just keep breaking matter in half he would eventually end up with the smallest bit of matter possible. This led to what we know as the atom. Solid Sphere Model His hypothesis: atoms are eternally unchanging and indivisible (he was not able to prove his thoughts due to lack of technology)

Models of the Atom 1803 John Dalton: And scientists that led us there! Father of Atomic Theory; First to show proof of atoms Experiment: He observed elements combine in whole number ratios to form compounds; Matter is NOT created or destroyed in chemical reactions. 1803 John Dalton: 4 Postulates of Theory: 1) all matter is made of atoms. Atoms are indivisible and indestructible. 2) All atoms of a given element are identical in mass and properties 3) Compounds are formed by a combination of two or more different elements 4) A chemical reaction is a rearrangement of atoms

Models of the ATOM Experiment: Zapped atoms with electricity And scientists that led us there! 1897 J.J. Thomson Experiment: Zapped atoms with electricity Conclusion: atoms consist of negatively charged electrons found inside positively-charged spheres; this is called the “plum pudding” model Plum Pudding Model

Rutherford discovered the nucleus Models of the ATOM And scientists that led us there! His experiment: gold-foil experiment using alpha particles Conclusion: atoms contain a small, massive, and positively-charged particle called a nucleus. 1911 Rutherford discovered the nucleus Which led to…

Models of the ATOM Solar System Model 1913 Bohr And scientists that led us there! Experiment: Observed light is given off when elements are exposed to flame or electric fields Conclusion: an atom consists of a dense, positively-charged nucleus, containing nearly all the atom’s mass, surrounded by electrons traveling in specific allowed orbits, like the planets around a star—sometimes called the “planetary” model. 1913 Bohr Solar System Model

Models of the ATOM 1927 Heisenberg And scientists that led us there! Proposed a cloud model of the atom— Experiment: “Thought experiment” He imagined a microscope that could an electron and to measure its position. He found that the electron's position and momentum did indeed obey the uncertainty relation he had derived mathematically Conclusions: Electrons are located in clouds, not neat orbits Tells you where the electron is most likely to be found (a matter of probability). Named the Uncertainty Principle 1927 Heisenberg

Models of the ATOM 1932 Chadwick And scientists that led us there! Discovered the neutron. Experiment: He followed up on the work performed by Ernest Rutherford. Chadwick bombarded alpha rays at beryllium. When struck, the beryllium emitted mysterious neutral rays. Conclusion: He reasoned that neutrons were important in holding the positively charged protons together

Quick Review

S 32.066 16 Atomic Number Atomic number: number of protons protons: positively charged; located in nucleus identifier for element; (change the number of protons, change the element) 16 S Sulfur 32.066

Atomic Mass Atomic Mass: average mass of element; weighted average Mass Number: sum of protons & neutrons; atom specific Neutrons: neutral charge; in nucleus 16 S Sulfur 32.066

How can we determine the number of Electrons? # of protons = # of electrons (in a neutral atom) Valence electrons: electrons in the outer most energy level; determines reactivity of element Valence electrons

Atomic Homework 6) sulfur-32 7) phosphorous-31 8) silver-109 9) calcium-41 10) lithium-7

Use the previous notes to fill in the blanks and answer the questions. # of protons = _____ # of electrons = _____ # of neutrons = _____ Identity of atom = ______ Are the # of protons & electrons equal? ______ # of protons = _____ # of electrons = _____ # of neutrons = _____ Identity of atom = ______ Are the # of protons & electrons equal? ______

ISOTOPES Isotope: atoms of the same elements with different number of neutrons ** Isotopes have different masses Mass Number: # of p+ + # of n O – specific to the isotope; may be different from mass on periodic table

Isotope Notation

Write the isotope notation for the three isotopes of Helium shown below.

Average Atomic Mass The average atomic mass is a weighted average mass of all the naturally occurring isotopes of an element based on the abundance of the element in nature.

Calculating Average Atomic Mass Formula: (Mass # I1)(%abundanceI1) + (Mass # I2)(%abundance I2) 100 Example: Hydrogen is 99% 1H, 0.8% 2H, and 0.2% 3H. (1)(99)+ (2)(.8)+(3)(.2) = 1.01 amu (rounded answer) I1 = isotope #1 I2 = isotope #2

OR… Calculating Average Atomic Mass by converting % to decimal first.

Practice Isotope mass (u) relative abundance Mg-24 23.985 0.7870